Method for producing p-type ZnO based compound semiconductor layer, method for producing ZnO based compound semiconductor element, and an n-type ZnO based compound semiconductor laminate structure

ABSTRACT

A method for producing a p-type ZnO based compound semiconductor layer including the steps of (a) supplying (i) Zn, (ii) O, (iii) optional Mg, and (iv) a Group 11 element which is Cu and/or Ag to form a Mg x Zn 1-x O (0≦x≦0.6) single crystal film doped with the Group 11 element; (b) supplying at least one Group 13 element selected from the group consisting of B, Ga, Al, and In on the Mg x Zn 1-x O (0≦x≦0.6) single crystal film; (c) alternately carrying out the steps (a) and (b) to form a laminate structure; and (d) annealing the laminate structure to form a p-type Mg x Zn 1-x O (0≦x≦0.6) layer co-doped with the Group 11 element and the Group 13 element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No.13/948,771 filed Jul. 23, 2013, the entire contents of which areincorporated by reference herein.

This application is based upon and claims the benefit of priority of theprior Japanese Patent Applications No. JP 2012-166833, No. JP2012-166834, No. JP 2012-166835, No. JP 2012-166836, No. JP 2012-166837,filed on Jul. 27, 2012, No. JP 2013-024013, filed on Feb. 12, 2013, andNo. JP 2013-036824, filed on Feb. 27, 2013, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

A) Field of the Invention

This invention relates to a method for producing a p-type ZnO basedcompound semiconductor layer and a method for producing a ZnO basedcompound semiconductor element. This invention also relates to a p-typeZnO based compound semiconductor single crystal layer, a ZnO basedcompound semiconductor element, and an n-type ZnO based compoundsemiconductor laminate structure.

B) Description of the Related Art

Zinc oxide (ZnO) is a direct transition-type semiconductor which has aband gap energy at room temperature of 3.37 eV, with a relatively highexciton binding energy of 60 meV. Use of zinc oxide has the advantage ofreduced raw material cost as well as smaller influence on environmentand human body. Accordingly, there is a high demand for a light-emittingdevice using ZnO having a high efficiency and low power consumption withreduced burden on environment.

However, the ZnO based compound semiconductor suffers from difficulty inrealizing p-type electroconductivity due to self-compensation effectcaused by the strong ionic property. For example, investigations havebeen conducted to develop a p-type ZnO based compound semiconductorhaving practical properties by using, for example, a Group 15 elementsuch as N, P, As, or Sb, a Group 1 element such as Li, Na, or K, and aGroup 11 element such as Cu, Ag, or Au as an acceptor impurity (see, forexample, Japanese Patent Application Laid Open Nos. 2001-48698,2001-68707, 2004-221132, and 2009-256142, and Japanese Patent No.4365530).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel method forproducing a p-type ZnO based compound semiconductor layer. Anotherobject of the present invention is to provide a method for producing aZnO based compound semiconductor element. Another object of the presentinvention is to provide a p-type ZnO based compound semiconductor singlecrystal layer, a ZnO based compound semiconductor element, and an n-typeZnO based compound semiconductor laminate structure.

According to an aspect of the present invention, there is provided amethod for producing a p-type ZnO based compound semiconductor layercomprising the steps of (a) preparing an n-type single crystal ZnO basedcompound semiconductor structure containing a Group 11 element which isCu and/or Ag and at least one Group 13 element selected from the groupconsisting of B, Ga, Al, and In; and (b) annealing the n-type singlecrystal ZnO based compound semiconductor structure to form a p-type ZnObased compound semiconductor layer co-doped with the Group 11 elementand the Group 13 element.

The present invention provides a novel method for producing a p-type ZnObased compound semiconductor layer, a method for producing a ZnO basedcompound semiconductor element, a p-type ZnO based compoundsemiconductor single crystal layer, a ZnO based compound semiconductorelement, and an n-type ZnO based compound semiconductor laminatestructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of an MBE apparatus.

FIG. 2A is a schematic cross sectional view of the specimen beforeannealing. FIG. 2B is a time chart of shutter sequence of Zn cell, Ocell, Ga cell, and Cu cell during formation of the alternate laminatestructure. FIG. 2C is a schematic cross sectional view of an alternatelaminate structure 54. FIG. 2D is a schematic cross sectional view of aGa-doped ZnO single crystal film 54 a and a Cu layer 54 b.

FIG. 3 shows graphs of CV properties and depth profile of impurityconcentration of the alternate laminate structure of the specimensbefore the annealing.

FIG. 4 shows graphs of CV properties and depth profile of impurityconcentration of the alternate laminate structure of the specimens afterthe annealing.

FIG. 5 shows graphs of depth profile of absolute concentration of Cu[Cu] and absolute concentration of Ga [Ga] after the annealing measuredby SIMS.

FIG. 6 shows graphs of CV properties and depth profile of impurityconcentration of the alternate laminate structure and its correspondingposition for Sample 5.

FIG. 7 shows graphs of depth profile of absolute concentration of Cu[Cu] and absolute concentration of Ga [Ga] after the annealing measuredby SIMS.

FIG. 8 shows graphs of electroconductivity, Cu concentration [Cu], Gaconcentration [Ga], and [Cu]/[Ga] value of the annealed alternatelaminate structure or its corresponding position.

FIGS. 9A, 9B, and 9D are schematic flow charts showing production methodof the ZnO based compound semiconductor light emitting element in theExamples. FIG. 9C is a schematic cross sectional view of thesemiconductor layer illustrating the formation of the p-type ZnO basedcompound semiconductor layer.

FIG. 10 is a flow chart showing a production method of the ZnO basedcompound semiconductor light emitting element by Example 1 from anotherpoint of view.

FIG. 11A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 2. FIG. 11B is a schematic cross sectional view of thealternate laminate structure 5A.

FIG. 12 is a time chart of an exemplary shutter sequence of Zn cell, Mgcell, O cell, Ga cell, and Cu cell during formation of the alternatelaminate structure.

FIG. 13A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 3. FIG. 13B is a schematic cross sectional view of anotherembodiment of active layer 15. FIG. 13C is a schematic cross sectionalview of the alternate laminate structure 16A.

FIG. 14 is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 4.

FIG. 15A is a schematic cross sectional view of the specimen beforeannealing of Sample 6. FIG. 15B is a time chart of shutter sequence ofZn cell, O cell, Cu cell, and Ga cell during formation of the alternatelaminate structure 64. FIG. 15C is a schematic cross sectional view ofan alternate laminate structure 64. FIG. 15D is a schematic crosssectional view of a Cu-doped ZnO single crystal film 64 a and Ga layer64 b.

FIGS. 16A and 16B are respectively graphs showing CV properties, depthprofile of the impurity concentration, and depth profile of [Cu] and[Ga] measured by SIMS of the alternate laminate structure of thespecimens before the annealing and the position where the alternatelaminate structure had been formed of the specimens after the annealingof Sample 6.

FIG. 17 shows RHEED images of p-type layer from [11-20] direction and[1-100] direction.

FIGS. 18A and 18B are respectively graphs showing CV properties, depthprofile of the impurity concentration, and depth profile of [Cu] and[Ga] measured by SIMS of the alternate laminate structure of thespecimens before the annealing and the position where the alternatelaminate structure had been formed of the specimens after the annealingof Sample 7.

FIGS. 19A and 19B are schematic flow charts of the production method ofZnO based compound semiconductor light emitting element according toExample 5.

FIG. 20A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 6. FIG. 20B is a schematic cross sectional view of analternate laminate structure 95A.

FIG. 21 is a time chart of an exemplary shutter sequence of Zn cell, Mgcell, O cell, Cu cell, and Ga cell during formation of the Cu and Gaco-doped p-type Mg_(x)Zn_(1-x)O (0<x≦0.6) single crystal layer andduring formation of the alternate laminate structure.

FIG. 22A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 7. FIG. 22B is a schematic cross sectional view of anotherembodiment of active layer 105. FIG. 22C is a schematic cross sectionalview of an alternate laminate structure 106A.

FIG. 23 is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 8.

FIG. 24 is a table summarizing conditions used in forming the Ga-dopedn-type Mg_(x)Zn_(1-x)O single crystal film in Examples 2 to 4.

FIG. 25 is a table summarizing conditions used in forming the Ga-dopedn-type Mg_(x)Zn_(1-x)O single crystal film in Examples 6 to 8.

DESCRIPTION OF EMBODIMENTS

First, the crystal formation apparatus used in the growth of ZnO basedcompound semiconductor film and the like is described. In theExperiments and Examples, the method used for the crystal formation ismolecular beam epitaxy (MBE). The ZnO based compound semiconductorcontains at least Zn and O.

FIG. 1 is a schematic cross sectional view illustrating MBE apparatus.The apparatus has a vacuum chamber 71, and a Zn source gun 72, an Osource gun 73, a Mg source gun 74, a Cu source gun 75, and a Ga sourcegun 76 are accommodated in the vacuum chamber 71.

The Zn source gun 72, the Mg source gun 74, the Cu source gun 75, andthe Ga source gun 76 respectively include Knudsen cell for accommodatingsolid source of Zn(7N), Mg(6N), Cu(9N), and Ga(7N), and Zn beam, Mgbeam, Cu beam, and Ga beam are ejected when the cell is heated.

The O source gun 73 includes an electrodeless discharge tube which usesa radio frequency wave of, for example, 13.56 MHz, and plasma isproduced in the electrodeless discharge tube from the O₂ gas (6N) andthe O radical beam is ejected. The discharge tube may be the oneprepared from alumina or high purity quartz.

A substrate 78 is held by a stage 77 having a substrate heater. Each ofthe source guns 72 to 76 is provided with a cell shutter, the substrate78 becomes irradiatable and non-irradiatable by the beam when the cellshutter is opened and closed. The substrate 78 is irradiated by the beamat the desired timing for the growth of the ZnO based compoundsemiconductor film having the desired composition.

The band gap can be increased by adding Mg to the ZnO. However, phaseseparation occurs when Mg composition is too high since ZnO has wurtzitestructure (hexagonal crystal) and MgO has rock salt structure (cubiccrystal). In the Mg_(x)Zn_(1-x)O where Mg composition in the MgZnO is x,x is preferably up to 0.6 to maintain the wurtzite structure. Therepresentation Mg_(x)Zn_(1-x)O includes ZnO with no addition of the Mgwherein x is 0.

n-type electroconductivity of the ZnO based compound semiconductor canbe realized without doping any impurities. However, the n-typeelectroconductivity can be increased by doping impurities such as Ga.p-type electroconductivity of the ZnO based compound semiconductor canbe realized by doping p-type impurities.

A thickness gauge 79 using a quartz oscillator is accommodated in thevacuum chamber 71, and flux intensity of each beam may be measured byfilm deposition rate measured by the thickness gauge 79.

The vacuum chamber 71 also has a gun 80 for reflection high energyelectron diffraction (RHEED) and a screen 81 for RHEED image. The RHEEDimage helps evaluation of surface evenness and growth mode of thecrystal layer formed on the substrate 78.

When the crystal growth is two dimensional epitaxial growth (singlecrystal growth) with flat surface, the RHEED image will exhibit a streakpattern, and when the crystal growth is three dimensional epitaxialgrowth (single crystal growth) with non-flat surface, the RHEED imagewill exhibit a spotted pattern. In the case of polycrystal growth, theRHEED image will exhibit a ring pattern.

Next, VI/II flux ratio in the Mg_(x)Zn_(1-x)O (0≦x≦0.6) crystal growthis explained, and in the explanation, J_(Zn) represents the fluxintensity of the Zn beam, J_(Mg) represents flux intensity of the Mgbeam, and J_(O) represents the flux intensity of the O radical beam. Thebeams of Zn and Mg which are metal materials are respectively beamscontaining Zn or Mg atoms or clusters of several Zn or Mg atoms. Bothatoms and clusters are effective for the crystal growth. The beam of Owhich is a gas material is a beam containing atom radical or neutralmolecule, and the flux intensity of O considered herein is the fluxintensity of the atom radical which is effective in the crystal growth.

k_(Zn) represents attachment coefficient of Zn which is probability ofthe Zn becoming attached to the crystal, k_(Mg) represents attachmentcoefficient of Mg which is probability of the Mg becoming attached tothe crystal, and k_(O) represents attachment coefficient of O which isprobability of the O becoming attached to the crystal. Productk_(Zn)J_(Zn) of the Zn attachment coefficient k_(Zn) and flux intensityJ_(Zn) and product k_(O)J_(O) of the 0 attachment coefficient k_(O) andthe flux intensity J_(O) respectively correspond to number of Zn atoms,Mg atoms, and O atoms which attaches to unit area of the substrate inunit time.

VI/II flux ratio is defined as the ratio of the k_(O)J_(O) to the sum ofk_(Zn)J_(Zn) and k_(Mg)J_(Mg), namely,k_(O)J_(O)/(k_(Zn)J_(Zn)+k_(Mg)J_(Mg)). The condition wherein VI/II fluxratio is less than 1 is referred to as “Group II rich condition” (orsimply “Zn rich condition” when Mg is not present), the conditionwherein VI/II flux ratio is equal to 1 is referred to as “stoichiometriccondition”, and the condition wherein VI/II flux ratio is greater than 1is referred to as “Group VI rich condition” (or “O rich condition”).

For the crystal growth on Zn face (+c face), attachment coefficientk_(Zn), k_(Mg), and k_(O) can be regarded 1 when surface temperature ofthe substrate is up to 850° C., and the VI/II flux ratio may berepresented by J_(O)/(J_(Zn)+J_(Mg)).

VI/II flux ratio can be calculated, for example, in the case of ZnOgrowth, by measuring the Zn flux as a Zn deposition speed F_(Zn) (nm/s)at room temperature by using a film thickness monitor using a quartzoscillator, and converting the F_(Zn) (nm/s) to the J_(Zn) (atoms/cm²s).

On the other hand, O radical flux may be calculated by irradiating the Oradical beam at a constant condition (for example, at an RF power of 300W and an O₂ flow rate of 2.0 sccm) while changing the Zn flux to allowthe ZnO growth; experimentally determining dependency of the ZnO growthrate on the Zn flux; fitting the results by using approximate expressionof the ZnO growth rate G_(ZnO):G_(ZnO)=[(k_(Zn)J_(Zn))⁻¹+(k_(O)J_(O))⁻¹]⁻¹ to thereby calculate Oradical flux J_(O) under such condition; and Calculating the VI/II fluxratio from the thus obtained Zn flux J_(Zn) and O radical flux J_(O).

The inventors of the present invention proposed a novel technique fordoping a ZnO based compound semiconductor with Cu in the related artapplication (Japanese Patent Application No. 2012-41096). This proposalis based on the experimental result that, when Zn, O, and Cu aresimultaneously supplied and a Cu-doped ZnO film is allowed to grow byMBE, a polycrystalline film with coarse surface is formed by threedimensional growth and Cu is not uniformly doped in the film thicknessdirection.

For such experimental results, the inventors of the present inventionconsidered that simultaneous feeding of the Zn, O, and Cu promoted thereaction between the active O radical and the Cu, and this resultedformation of different crystalline phase of CuO at a pace higher thanthe substitution of the Zn site by the Cu and this invited ZnO growthinhibition, and hence, polycrystallization.

The inventors considered that, when Zn, O radical, and Cu aresimultaneously supplied in the in the growth of the Cu-doped ZnO film,formation of the CuO(II) is facilitated since Cu readily reacts with theactive O radical, and formation of the divalent Cu²⁺ will be dominant.In addition, since thermal decomposition of the CuO(II) into Cu₂O(I)occurs at a temperature higher than the temperature of the Cu-doped ZnOfilm growth, it was estimated that the divalent Cu²⁺ is less likely tobe converted into the monovalent Cu⁺, and hence, Cu which does notfunction as an acceptor in the ZnO will be dominant.

The inventors of the present invention considered that a method formingthe Cu-doped ZnO layer wherein monovalent Cu⁺ is more likely to beformed than the divalent Cu²⁺ and Cu readily substitutes the Zn sitesshould facilitate two dimensional growth and p-type electroconductivity,and proposed in this related art application a production method of theCu-doped p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) layer, for example, byalternately repeating the cycle of forming a Mg_(x)Zn_(1-x)O (0≦x≦0.6)single crystal film and supplying Cu on the Mg_(x)Zn_(1-x)O (0≦x≦0.6)single crystal film. The production method according to the related artis capable of producing a Cu-doped p-type Mg_(x)Zn_(1-x)O single crystallayer with improved evenness and crystallinity.

The invention of this application relates to a production method of thep-type ZnO based compound semiconductor film and a production method ofthe ZnO based compound semiconductor element different from the oneproposed in the related art application, and in the present invention,the p-type ZnO based compound semiconductor layer is produced, forexample, by a method comprising the steps of preparing a single crystaln-type ZnO based compound semiconductor structure containing a Group 11element which is Cu and/or Ag and at least one Group 13 element selectedfrom the group consisting of B, Ga, Al, and In; and annealing the singlecrystal n-type ZnO based compound semiconductor to form a p-type ZnObased compound semiconductor layer co-doped with the Group 11 elementand the Group 13 element. In the production method according to thepresent invention, the monovalent Cu⁺ formed functions as an acceptor atan efficiency higher than the related art proposal.

First, the first experiment of the inventors of the present invention isdescribed. The inventors of the present invention found that theGa-doped ZnO single crystal film having Cu supplied on the film (thealternate laminate structure) is converted to a p-type film byannealing. The experiment will be described for four samples, namely,Sample 1 to Sample 4, and in the following description, the specimenbefore the annealing is referred to as the pre-annealing specimen andthe specimen after staring the annealing is referred to as thepost-annealing specimen.

The method used for preparing the pre-annealing specimen of Sample 1 isdescribed. FIG. 2A is a schematic cross sectional view of thepre-annealing specimen.

A Zn face ZnO (0001) substrate (hereinafter referred to as the ZnOsubstrate) 51 having n-type electroconductivity was thermally cleaned at900° C. for 30 minutes, and the temperature of the substrate 51 wasreduced to 300° C. At this temperature (growth temperature, 300° C.), aZnO buffer layer 52 having a thickness of 30 nm was deposited on the ZnOsubstrate 51 by using the Zn flux F_(Zn) at 0.17 nm/s (J_(Zn)=1.1×10¹⁵atoms/cm²s) and the O radical beam at an RF power of 300 W and an O₂flow rate of 2.0 sccm (J_(O)=8.1×10¹⁴ atoms/cm²s). Annealing was thenconducted at 900° C. for 10 minutes for improvement of crystallinity andsurface evenness of the ZnO buffer layer 52.

On this ZnO buffer layer 52, an undoped ZnO layer 53 having a thickness100 nm was deposited at a growth temperature of 900° C. by using a Znflux F_(Zn) of 0.17 nm/s (J_(Zn), =1.1×10¹⁵ atoms/cm²s) and the Oradical beam at an RF power of 300 W and an O₂ flow rate of 2.0 sccm(J_(O)=8.1×10¹⁴ atoms/cm²s). This undoped ZnO layer 53 was an n-type ZnOlayer. Zn, 0, and Ga were supplied at a timing different from Cu on theundoped ZnO layer 53 to form an alternate laminate structure 54. Thealternate laminate structure 54 was formed at a temperature of 300° C.

FIG. 2B is a time chart showing shutter sequence of the Zn cell, the Ocell, the Ga cell, and the Cu cell in forming the alternate laminatestructure.

In forming the alternate laminate structure 54, the step of forming theGa-doped ZnO single crystal film by opening the Zn cell shutter, the Ocell shutter, and the Ga cell shutter and closing the Cu cell shutterand the step of Cu attachment (the step of forming the Cu layer) byclosing the Zn cell shutter, the 0 cell shutter, and the Ga cell shutterand opening the Cu cell shutter were alternately repeated. Since thestep of forming the Ga-doped ZnO single crystal film and the step ofattaching Cu on the Ga-doped ZnO single crystal film is separatelyconducted with no overlap between the period when the O cell shutter isopen and the period when the Cu cell shutter is open, the O radical andthe Cu will not be simultaneously supplied.

In the step of forming the Ga-doped ZnO single crystal film, the openingand closing the O cell shutter and the Ga cell shutter aresimultaneously conducted, and the Zn cell shutter is opened beforeopening the O cell shutter and the Ga cell shutter and closed afterclosing the O cell shutter and the Ga cell shutter, and in other words,the open period of the Zn cell shutter include the open period of the Ocell shutter and the Ga cell shutter. Since the O radical the Cu are notsimultaneously supplied and the surface of the Ga-doped ZnO singlecrystal film is covered by Zn before and after the Cu attachment step(thereby inhibiting the exposure of the O), direct reaction between theO radical and the Cu is prevented.

In the preparation of the pre-annealing specimen of Sample 1, the openperiod of the O cell shutter and the Ga cell shutter was 16 seconds foreach opening, and the open period of the Zn cell shutter was extended 1second before and after the open period of the O cell shutter and the Gacell shutter. The open period of the Zn cell shutter was 18 seconds foreach opening, and the 16 second period when all of the Zn cell shutter,the O cell shutter, and the Ga cell shutter were open was the periodallowed for each Ga-doped ZnO single crystal film growth period. Theopen period of the Cu cell shutter was 10 seconds for each opening.

Each of the step of forming the Ga-doped ZnO single crystal film and theCu attachment step were alternately repeated for 140 times to depositthe alternate laminate structure 54 having a thickness of 480 nm. In theformation of the Ga-doped ZnO single crystal film, the Zn flux F_(Zn)was 0.17 nm/s (J_(Zn)=1.1×10¹⁵ atoms/cm²s), the O radical beam wasirradiated at an RF power 300 W and an O₂ flow rate 2.0 sccm(J_(O)=8.1×10¹⁴ atoms/cm²s), and the Ga cell temperature T_(Ga) was 490°C. VI/II flux ratio was 0.74 (Zn rich condition). In the Cu attachmentstep, the Cu cell temperature T_(c), was 930° C., and the Cu flux F_(Cu)was 0.0015 nm/s.

FIG. 2C is a schematic cross sectional view of the alternate laminatestructure 54. The alternate laminate structure 54 has a structurewherein a Ga-doped ZnO single crystal films 54 a and a Cu layers 54 bare alternately laminated one on another. This laminate structure mayalso be regarded as a laminate structure comprising 140 layers of theGa-doped ZnO single crystal films 54 a each having the Cu suppliedthereon disposed one on another in thickness direction.

The Ga-doped ZnO single crystal film 54 a has a thickness ofapproximately 3.3 nm, and the Cu layer 54 b has a thickness (Cuattachment thickness) of up to 1 atomic layer, for example, about 1/20atomic layer. In this case, Cu coverage of the surface of the Ga-dopedZnO single crystal film 54 a will be approximately 5%.

FIG. 2D is a schematic cross sectional view of the Ga-doped ZnO singlecrystal film 54 a and the Cu layer 54 b. For example, the Cu layer 54 bhaving a thickness of about 1/20 atomic layer is formed by Cu attachedto a part of the surface of the Ga-doped ZnO single crystal film 54 a asshown in FIG. 2D. For the simplicity of the drawing, the alternatelaminate structure is shown by the layer structure of FIG. 2C includingsuch embodiment of Cu attachment.

FIG. 3 shows graphs of CV profile and depth profile of the impurityconcentration of the alternate laminate structure for the pre-annealingspecimens. The upper graph is the one showing the CV profile and thelower graph is the one showing the depth profile. The measurement wasconducted by ECV using the electrolyte for the Schottky electrode, andthe graph shows the results analyzed by parallel model. The leftmostgraphs are those for Sample 1, and in FIG. 3, graphs for Sample 1 toSample 4 are shown from left to right including the samples that will bedescribed below. In the graph showing the CV profile, the x axisrepresents voltage (unit, “V”) and the y axis represents “1/C²” (unit,“cm⁴/F²”). Both axes are in linear scale. In the graph showing the depthprofile, x axis represents position (unit “nm”) in the depth (thickness)direction of the specimen. The y axis represents the impurityconcentration (unit, “cm⁻³”). In this graph, the x axis is in linearscale and the y axis is in logarithmic scale.

With regard to the graph showing the CV profile of Sample 1, the curverises upward to the right (namely, 1/C² increases with the increase inthe voltage), and this means that the Ga-doped ZnO single crystal film54 a with Cu supplied on the film surface (the alternate laminatestructure 54) has n-type electroconductivity. It is to be noted that theinclination corresponds to the value of resistance.

With regard to the graph showing the depth profile of Sample 1, impurityconcentration (donor concentration) N_(d) in the alternate laminatestructure 54 of the pre-annealing specimen of Sample 1 is 1.0×10²⁰ cm⁻³.

Next, annealing of the Sample 1 was conducted in the atmosphere at 650°C. for 30 minutes. After this annealing, annealing at the sametemperature but for 10 minutes was repeated four times.

FIG. 4 shows graphs depicting CV profile and depth profile of theimpurity concentration of the post-annealing specimens. The CV profileand the depth profile of the position where the alternate laminatestructure 54 had been formed are shown in the graph. The leftmost graphsare those for Sample 1, and as in the case of FIG. 3, graphs for thepost-annealing specimens of Sample 1 to Sample 4 are shown from left toright including the samples that will be described below.

With regard to the column of Sample 1, the graph in the upper row showsthe CV profile after annealing at 650° C. for 30 minutes, and the x andy axes are the same as the graph of the CV profile in FIG. 3. Comparedwith the pre-annealing specimen, resistance is higher at the positionwhere the alternate laminate structure 54 (the Ga-doped ZnO singlecrystal film 54 a having Cu supplied on the film surface) had beenformed, and conceivably, this is due to the functioning of the Cu as ap-type impurity which reduces the functions of the Ga which is an n-typeimpurity.

In the lower part of the column, two graphs are shown which respectivelydepict the CV profile (upper graph) and the depth profile (lower graph)of the specimen which has been annealed once at 650° C. for 30 minutes,and then four times at 650° C. for 10 minutes, namely 70 minutes intotal. The x and y axes of the graphs are the same as those in thegraphs of FIG. 3.

In the upper graph showing the CV profile, the curve drops downward tothe right (namely, 1/C² decreases with the increase in the voltage), andthis means that the position where the alternate laminate structure 54had been formed has p-type electroconductivity. Cu concentration perunit volume at the position where the alternate laminate structure 54had been formed is higher than the Ga concentration, and this indicatesthat the dispersion of the Cu first results in the compensation of theGa, and then, in the increase of the concentration of the p-typeimpurity. The lower graph showing the depth profile indicates that theimpurity concentration (acceptor concentration) N_(a) of the positionwhere the alternate laminate structure 54 had been formed of thepost-annealing specimen of Sample 1 is 2.0×10¹⁷ cm⁻³ to 1.0×10¹⁹ cm⁻³.

FIG. 5 shows graphs of depth profile of the absolute concentration of Cu[Cu] and the absolute concentration of Ga [Ga] after the annealingmeasured by secondary ion mass spectrometry (SIMS). The leftmost graphsare those for Sample 1, and in FIG. 5, graphs for post-annealingspecimens of Sample 1 to Sample 4 are shown from left to right includingthe samples that will be described below. In the graph, the x axisrepresents position in the depth direction of the post-annealingspecimen and the y axis represents the Cu concentration [Cu] and the Gaconcentration [Ga]. The position in the depth direction of thepost-annealing specimen is by the unit “μm” for Sample 1 to Sample 3,and “nm” for Sample 4. Unit of the [Cu] and [Ga] is “cm⁻³”.

With regard to the column of Sample 1, the range in the depth of 0.0 μmto 0.48 μm is the position wherein a p-type layer has been formedcorresponding to the position where alternate laminate structure 54 hadbeen formed. The Cu concentration [Cu] is 2.2×10²⁰ cm⁻³, and the Gaconcentration [Ga] is 3.4×10¹⁹ cm⁻³, and as indicated in the graph, bothare approximately constant through the thickness of the p-type layer.The term “approximately constant” used herein means that theconcentration is within the range of 50% to 150% of the averageconcentration (2.2×10²⁰ cm⁻³ in the case of [Cu] of Sample 1). Cu isevenly distributed. [Cu] is higher than [Ga], and the ratio of [Cu] to[Ga] (namely, the value of [Cu]/[Ga]) is 6.5. It is to be noted that the[Cu] and [Ga] may not be accurately measured near the surface of thep-type layer, for example, due to the matters adsorbed on the surface.For example, a lower value is measured in the case of Sample 1.

Next, Sample 2 to Sample 4 are described. Samples 2 to 4 are samplesprepared by adjusting the amount of Cu and Ga supplied during theproduction of the alternate laminate structure, and the value of[Cu]/[Ga] is different in each of Samples 2 to 4 from Sample 1.

The pre-annealing specimen of Samples 2 to 4 is similar to Sample 1shown in FIG. 2A in that a ZnO buffer layer, an undoped ZnO layer, andan alternate laminate structure are disposed on the ZnO substrate 51 inthis order. Samples 2 to 4, however, are different from Sample 1 in theconditions used for depositing the layers disposed on the ZnO substrate51.

In the preparation of pre-annealing specimens of Samples 2 and 3, theZnO buffer layer was deposited at a temperature of 300° C. and growthperiod of 5 minutes. More specifically, the ZnO buffer layer having athickness of 40 nm was deposited by using a Zn flux F_(Zn) of 0.16 nm/s,and irradiating the O radical beam at an RF power of 300 W and an O₂flow rate of 2.0 sccm. Annealing was then conducted at 900° C. for 15minutes.

The undoped ZnO layer was deposited at a temperature of 900° C. andgrowth period of 15 minutes. More specifically, the undoped ZnO layerhaving a thickness of 120 nm was deposited by using a Zn flux F_(Zn) of0.16 nm/s, and irradiating the O radical beam at an RF power of 300 Wand the O₂ flow rate of 2.0 sccm.

The alternate laminate structure was deposited at a temperature 300° C.The Ga-doped ZnO single crystal film was deposited by using a Zn fluxF_(Zn) of 0.16 nm/s, and irradiating the O radical beam at an RF powerof 300 W and an O₂ flow rate of 2.0 sccm. The VI/II flux ratio was lessthan 1 corresponding to the Zn rich conditions. Ga cell temperatureT_(Ga) was 498° C. in the preparation of Sample 2, and 505° C. in thepreparation of Sample 3. Each growth period for Ga-doped ZnO singlecrystal film was set at 16 seconds. The cell temperature in Cuattachment step T_(Cu), was 930° C., and the Cu flux F_(Cu) was 0.0015nm/s. Each open period for the Cu cell shutter was 10 seconds. The stepof depositing the Ga-doped ZnO single crystal film and the Cu attachmentstep were alternately repeated 60 times to produce the alternatelaminate structure. The growth period was 30 minutes. The alternatelaminate structure had a thickness of 207 nm in Sample 2, and 199 nm inSample 3. The pre-annealing specimens of Samples 2 and 3 were therebyprepared.

The method used for preparing the pre-annealing specimen of Sample 4 isdifferent from those of Samples 2 and 3 in the conditions used in thedeposition of the alternate laminate structure.

The alternate laminate structure of Sample 4 was formed at a temperatureof 300° C. The Ga-doped ZnO single crystal film was deposited by using aZn flux F_(Zn) of 0.15 nm/s, and irradiating the O radical beam at an RFpower of 300 W and an O₂ flow rate of 2.0 sccm. The VI/II flux ratio wasless than 1 corresponding to the Zn rich conditions. Ga cell temperatureT_(Ga) was 525° C. The growth period for Ga-doped ZnO single crystalfilm was set at 16 seconds. The cell temperature in Cu attachment stepT_(Cu) was 930° C., and the Cu flux F_(Cu) was 0.0015 nm/s. Each openperiod for the Cu cell shutter was 50 seconds. Each of the step ofdepositing the Ga-doped ZnO single crystal film and the Cu attachmentstep were alternately repeated 30 times to produce the alternatelaminate structure having a thickness of 90 nm. The pre-annealingspecimen of Sample 4 was thereby prepared.

With regard to the columns of Samples 2 to 4 in FIG. 3, the upper graphshowing the CV profile demonstrates that the alternate laminatestructure experiences increase in the 1/C² with the increase in thevoltage in Samples 2 to 4 as in the case of Sample 1. This in turn meansthat the alternate laminate structure (the Ga-doped ZnO single crystalfilm having Cu supplied on the film) of the pre-annealing specimen ofSamples 2 to 4 has n-type electroconductivity.

The lower graphs showing the depth profile indicate that the donorconcentration N_(d) of the alternate laminate structure in Samples 2, 3,and 4 are respectively 1.0×10²⁰ cm⁻³, 1.0×10²⁰ cm⁻³, and 7.0×10²⁰ cm⁻³.

Samples 2 to 4 were subsequently subjected to annealing.

With regard to the column of Sample 2 in FIG. 4, Sample 2 was dividedinto 2 parts, and one was subjected to annealing in the atmosphere at650° C. for 10 minutes, and the other was subjected to annealing in theatmosphere at 650° C. for 30 minutes. The graph in the upper row showsCV profile of Sample 2 which has been subjected to the annealing at 650°C. for 10 minutes. At the position where the alternate laminatestructure 54 (the Ga-doped ZnO single crystal film having Cu supplied onthe film surface) had been formed, the resistance is higher compared tothe pre-annealing resistance.

The graphs in the lower row respectively show the CV profile and thedepth profile of the impurity concentration for Sample 2 which has beensubjected to the annealing at 650° C. for 30 minutes.

In the upper graph showing the CV profile, 1/C² decreases with theincrease in the voltage, and this indicates that the position where thealternate laminate structure had been formed has changed to p-type. Thelower graph showing the depth profile demonstrates that the acceptorconcentration N_(a) at the position where the alternate laminatestructure had been formed in Sample 2 which had been subjected to theannealing at 650° C. for 30 minutes is 1.0×10¹⁷ cm⁻³ to 7.0×10¹⁸ cm⁻³.

The graph in the column of Sample 2 in FIG. 5 depicts depth profile ofCu concentration [Cu] and Ga concentration [Ga] of the specimen whichhas been annealed at 650° C. for 30 minutes measured by SIMS. In therange corresponding to the position where the alternate laminatestructure had been formed (the position where p-type layer has beenformed), the Cu concentration [Cu] is 1.7×10²⁰ cm⁻³, the Gaconcentration [Ga] id 3.7×10¹⁹ cm⁻³, and both are approximately constantthrough the thickness of the p-type layer. The [Cu]/[Ga] value is 4.6.

With regard to the column of Sample 3 in FIG. 4, Sample 4 was alsoannealed in the atmosphere. The annealing was conducted 7 times at 550°C. for 10 minutes, 4 times at 570° C. for 10 minutes, 3 times at 580° C.for 10 minutes, and once at 580° C. for 5 minutes, and then 590° C. for12 minutes. The total annealing time was 157 minutes.

The graph in the upper row is a graph showing CV profile afterconducting the annealing 3 times at 550° C. for 10 minutes (totalannealing time, 30 minutes). Resistance of the position where thealternate laminate structure had been formed has increased compared withthe resistance before the annealing.

The graphs in the lower row respectively show the CV profile and thedepth profile of the impurity concentration for Sample 3 which has beensubjected to the annealing at 590° C. for 12 minutes (total annealingtime, 157 minutes).

In the upper graph showing the CV profile, 1/C² decreases with theincrease in the voltage, and this indicates that the position where thealternate laminate structure had been formed has changed to p-type. Thelower graph showing the depth profile demonstrates that the acceptorconcentration N_(a) at the position where the alternate laminatestructure had been formed in the post-annealing specimen of Sample 3 is6.0×10¹⁷ cm⁻³ to 1.0×10¹⁹ cm⁻³.

With regard to the column of Sample 3 in FIG. 5, the range correspondingto the position where the alternate laminate structure has been formed(the position where p-type layer has been formed) has a Cu concentration[Cu] of 1.2×10²⁰ cm⁻³ and a Ga concentration [Ga] of 6.0×10¹⁹ cm⁻³, andboth are approximately constant through the thickness of the p-typelayer. The value of [Cu]/[Ga] is 2.0.

With regard to the column of Sample 4 in FIG. 4, Sample 4 was preparedby conducting the annealing in the atmosphere at 500° C. for 10 minutes,at 525° C. for 10 minutes, and at 550° C. for 10 minutes, and thenrepeating the annealing 5 times at 600° C. for 10 minutes. The totalannealing time was 80 minutes.

The graph in the upper row shows CV profile after the annealing at 550°C. for 10 minutes. At the position where the alternate laminatestructure had been formed, the resistance is higher compared to thepre-annealing resistance.

The graphs in the lower row respectively show the CV profile and thedepth profile of the impurity concentration for the specimen after theannealing at 600° C. for 50 minutes (the annealing of 10 minutes for 5times) (80 minutes annealing in total).

In the upper graph showing the CV profile, 1/C² decreases with theincrease in the voltage, and this indicates that the position where thealternate laminate structure had been formed has changed to p-type. Thelower graph showing the depth profile demonstrates that the acceptorconcentration N_(a) at the position where the alternate laminatestructure had been formed in the post-annealing specimen of Sample 4 is8.0×10¹⁷ cm⁻³ to 1.0×10¹⁹ cm⁻³.

With regard to the column of Sample 4 in FIG. 5, the Cu concentration[Cu] in the range corresponding to the position where the alternatelaminate structure had been formed (the position where p-type layer hasbeen formed) is 3.5×10²⁰ cm⁻³, and the Ga concentration [Ga] is 2.0×10²⁰cm⁻³, and both are approximately constant in the thickness of the p-typelayer. The [Cu]/[Ga] value is 1.8.

Next, Sample 5 is explained.

The pre-annealing specimen of Sample 5 is similar to Sample 1 shown inFIG. 2A in that the ZnO buffer layer 52, the undoped ZnO layer 53, andthe alternate laminate structure are disposed on the ZnO substrate 51 inthis order. Sample 5, however, is different from Sample 1 in theconditions used for depositing the alternate laminate structure.

The alternate laminate structure of Sample 5 was deposited at atemperature of 300° C. In the deposition of the Ga-doped ZnO singlecrystal film, Zn flux F_(2n) was 0.15 nm/s (J_(Zn)=9.9×10¹⁴ atoms/cm²s),and the O radical beam was irradiated at an RF power of 300 W and an O₂flow rate of 2.0 sccm (J_(O)=8.1×10¹⁴ atoms/cm²s). The VI/II flux ratiowas 0.82. The Ga cell temperature T_(Ga) was 530° C. Each growth periodfor Ga-doped ZnO single crystal film was set at 16 seconds. The celltemperature in Cu attachment step T_(Cu) was 890° C., and the Cu fluxF_(Cu) was 0.001 nm/s. Each open period for the Cu cell shutter was 80seconds. Each of the step of depositing the Ga-doped ZnO single crystalfilm and the Cu attachment step were alternately repeated 30 times toproduce the alternate laminate structure having a thickness of 80 nm.

Sample 5 was divided into 3 parts, and these parts were annealed inoxygen atmosphere at an O₂ flow rate of 1 L/min for 10 minutesrespectively at an annealing temperature of 600° C., 620° C., and 630°C.

FIG. 6 shows graphs of the CV profile and the depth profile of theimpurity concentration for the alternate laminate structure and itscorresponding position of Sample 5. The graphs in the lower rowrespectively represents graphs of the CV profile, and graphs in thelower row respectively represents graphs of the depth profile. From leftto right, the graphs are for the pre-annealing specimen and thepost-annealing specimens annealed at 600° C., 620° C., and 630° C. The xand y axes are the same as the graphs shown in the lower column of FIGS.3 and 4.

In the graph of the CV profile of the pre-annealing specimen, 1/C²increases with the increase in the voltage, and this indicates that thealternate laminate structure has n-type electroconductivity. As shown inthe graph of depth profile, the impurity concentration (donorconcentration) N_(d) of the pre-annealing specimen is 1.0×10²¹ cm⁻³ to2.0×10²¹ cm⁻³.

In the graph showing the CV profile of the specimen annealed at 600° C.,1/C² decreases with the increase in the voltage, indicating that theposition where the alternate laminate structure had been formed hasbecome p-type. The graph in the lower row shows that the impurityconcentration (acceptor concentration) N_(a) at the position where thealternate laminate structure had been formed is 1.0×10¹⁸ cm⁻³ to2.0×10¹⁸ cm⁻³.

In the graph showing the CV profile of the specimen annealed at 620° C.,1/C² also decreases with the increase in the voltage, indicating thatthe position where the alternate laminate structure had been formed hasbecome p-type. The graph of the depth profile shows that the acceptorconcentration N_(a) at the position where the alternate laminatestructure had been formed is 3.0×10¹⁸ cm⁻³ to 4.0×10¹⁸ cm⁻³.

In the case of the graph showing the CV profile of the specimen annealedat 630° C. for 10 minutes, 1/C² increases with the decrease in thevoltage, indicating that the position where the alternate laminatestructure had been formed has n-type electroconductivity. As a result ofexcessive annealing, the position where the alternate laminate structurehad been formed which had become p-type again became an n-type layer.The graph of the depth profile shows that the donor concentration N_(d)at the position where the alternate laminate structure had been formedis 2.0×10¹⁹ cm⁻³ to 3.0×10¹⁹ cm⁻³.

FIG. 7 shows graphs depicting depth profile of the absoluteconcentration of Cu [Cu] and the absolute concentration of Ga [Ga]measured by SIMS. The graphs showing the depth profile of thepre-annealing specimen and the specimens respectively annealed at 600°C., 620° C., and 630° C. are shown from left to right. In the graph, thex axis represents position in the depth direction by the unit of “nm”while the y axis represents the Cu concentration [Cu] and the Gaconcentration [Ga] by the unit of “cm⁻³”. The range in the depth of 0 nmto 80 nm corresponds to the alternate laminate structure and itscorresponding position.

In the alternate laminate structure of the pre-annealing specimen, theCu concentration [Cu] is 7.2×10²⁰ cm⁻³, the Ga concentration [Ga] is4.1×10²⁰ cm⁻³, and the [Cu]/[Ga] is 1.75.

In the position corresponding to the position where the alternatelaminate structure had been formed (the position where p-type layer hasbeen formed) of the specimen annealed at 600° C., the Cu concentration[Cu] is 4.8×10²⁰ cm⁻³, the Ga concentration [Ga] is 3.8×10²⁰ cm⁻³, andboth are approximately constant through the thickness of the p-typelayer. The value of [Cu]/[Ga] value is 1.26.

In the position corresponding to the position where the alternatelaminate structure had been formed (the position where p-type layer hasbeen formed) of the specimen annealed at 620° C., the Cu concentration[Cu] is 3.8×10²⁰ cm⁻³, the Ga concentration [Ga] is 4.1×10²⁰ cm⁻³, andboth are approximately constant through the thickness of the p-typelayer. The value of [Cu]/[Ga] value is 0.93.

In the position corresponding to the position where the alternatelaminate structure had been formed of the specimen annealed at 630° C.,the Cu concentration [Cu] is 4.2×10²⁰ cm⁻³, the Ga concentration [Ga] is4.8×10²⁰ cm⁻³, and the value of [Cu]/[Ga] value is 0.88.

The value of [Cu]/[Ga] changes before and after the annealing, forexample, by the diffusion of the Cu and Ga to the exterior of thealternate laminate structure. Compared to Ga, Cu is more likely to bediffused, and the value of [Cu]/[Ga] after the annealing would besmaller than the value before the annealing. The value of [Cu]/[Ga]after the annealing varies by the temperature used in the annealing, and[Cu]/[Ga] is likely to decrease with the increase in the annealingtemperature. The [Cu]/[Ga] will also change by other conditions of theannealing such as annealing time.

FIG. 8 is a graph showing electroconductivity, Cu concentration [Cu], Gaconcentration [Ga], and [Cu]/[Ga] value of the position corresponding tothe annealed alternate laminate structure, and this graph includes notonly Samples 1 to 5 but also other experimental samples conducted by theinventors of the present invention. In the graph, the x axis representsCu concentration [Cu] by the unit “cm⁻³” and the y axis represents Gaconcentration [Ga] by the unit “cm⁻³”. Both axes are in logarithmicscale. Solid (black) circles represent samples which became p-type afterthe annealing and solid diamonds represent samples which failed to bep-type despite increase in its resistance.

The sample indicated by a is the sample which became p-type at the valueof the [Cu]/[Ga] of 0.93 (Sample 5 annealed at 620° C.). For this samplerepresented by a, the Cu concentration [Cu] is 3.8×10²⁰ cm⁻³, and the Gaconcentration [Ga] is 4.1×10²⁰ cm⁻³.

The sample indicated by β is the sample which became p-type at the valueof the [Cu]/[Ga] of 1.0. For this sample represented by β, both the Cuconcentration [Cu] and the Ga concentration [Ga] are 3.0×10²⁰ cm⁻³.

The sample indicated by γ is the sample which failed to become p-type atthe value of [Cu]/[Ga] of 0.93. For this sample represented by γ, the Cuconcentration [Cu] is 3.8×10¹⁹ cm⁻³, and the Ga concentration [Ga] is4.1×10¹⁹ cm⁻³.

Samples α and γ are different in their Cu concentration [Cu] and Gaconcentration [Ga] by one order of magnitude, and comparison of thesesamples indicate that even if the value of [Cu]/[Ga] value were equal(0.93), conversion into the p-type depends on the absolute values of theconcentration ([Cu] and [Ga]).

Although not plotted in the graph, a sample with p-type was obtained atthe Cu concentration [Cu] of 5.87×10²⁰ cm⁻³, the Ga concentration [Ga]of 6.44×10²⁰ cm⁻³, and the [Cu]/[Ga] value of 0.91. Conversion to thep-type seems to be possible at the [Cu]/[Ga] value of 0.90 or higher.

The experiments as described above conducted by the inventors of thepresent invention demonstrate that the alternate laminate structure(Ga-doped ZnO single crystal film) of Samples 1 to 5 is n-type in itsas-grown state (see FIGS. 3 and 6), and when annealed, it is convertedto p-type (see lower column of FIG. 4 and FIG. 6) after experiencingincrease in the resistance (see upper column of FIG. 4). As a result ofthe annealing, Cu in the Cu layer evenly diffuses in the interior of theGa-doped ZnO single crystal film, and conceivably, this Cu diffusion(generation of Cu⁺ functioning as an acceptor) results in the increaseof the resistance (decrease of the donor concentration N_(d)) of thealternate laminate structure (Ga-doped ZnO single crystal film), andhence, generation of the p-type ZnO single crystal layer co-doped withCu ad Ga.

Comparison of Samples 1 to 5 indicates that conditions in the annealingrequired for conversion into the p-type (for example, temperature, time,and atmosphere) are likely to be different by the thickness of thealternate laminate structure and the Ga-doped ZnO single crystal, the Cuconcentration [Cu], the Ga concentration [Ga], and the ratio of [Cu] to[Ga] ([Cu]/[Ga]) of the alternate laminate structure, and the like.

With regard to the value of [Cu]/[Ga] in Samples 1 to 3 wherein the Cuconcentration [Cu] and the Ga concentration [Ga] are respectively withinnarrow ranges, the value of [Cu]/[Ga] is in the relation: Sample1>Sample 2>Sample 3, and temperature or time of the annealing requiredfor conversion to p-type decreases with the decrease in the [Cu]/[Ga]value. The value of [Cu]/[Ga] is, for example, preferably less than 100,and more preferably up to 50 in consideration of the risk of, forexample, formation of donor-type point defect such as oxygen vacancy byhigh temperature annealing, decrease in the Cu concentration and the Gaconcentration in the p-type layer associated with diffusion of Cu and Gato the exterior of the p-type layer, and loss of steepness at the p-ninterface associated with the diffusion of the Cu and the Ga to theunderlying layer (n-type layer).

In addition, if it is conceived that Cu and Ga are compensated at Cu:Gaof 1:1 in the alternate laminate structure (the structure comprising theGa-doped ZnO single crystal film and the Cu supplied on the filmsurface), conversion to p-type should be possible when [Cu]/[Ga]>1. Theexperiments, however, demonstrated that, if Cu and Ga are suppliedduring the formation of the alternate laminate structure so that thevalue of [Cu]/[Ga] at the position corresponding to the alternatelaminate structure after the annealing is 0.9 or higher, the alternatelaminate structure can be converted to p-type. The p-typeelectroconductivity of practical level is more likely to be obtained,for example, when the [Cu]/[Ga]≧2.

Accordingly, when the value of [Cu]/[Ga] at the position correspondingto the alternate laminate structure after the annealing is 0.9[Cu]/[Ga]<100, the alternate laminate structure can be converted to thep-type by annealing at a relatively low temperature, and when the valueis 2≦[Cu]/[Ga]≦50, the p-type electroconductivity of practical level maybe realized by annealing at an even lower temperature.

In the experiment, a p-type layer having a approximately constant Cuconcentration [Cu] and a approximately constant Ga concentration [Ga]through the thickness was obtained as shown, for example, in FIG. 5. TheCu concentration [Cu] in the p-type layer was 1.2×10²⁰ cm⁻³ (in the caseof Sample 3) to 4.8×10²⁰ cm⁻³ (in the case of Sample 5 annealed at 600°C.).

These results indicate that, Cu can be evenly doped in the thicknessdirection at least to a concentration of less than 1.0×10²¹ cm⁻³ so thatthe Cu will be at a concentration high enough, namely, at 1.0×10¹⁹ cm⁻³or higher, for example, by the method of annealing the Ga-doped n-typeZnO single crystal film having Cu supplied on the film surface.

The inventors of the present invention has found after an intensivestudy that, in the ZnO based compound semiconductor layer, Cu impurityconcentration (acceptor concentration) is about 2 orders of magnitudelower than Cu absolute concentration [Cu]. In consideration of thisfinding, a p-type layer having an acceptor concentration of at least1.0×10¹⁷ cm⁻³ and less than 1.0×10¹⁹ cm⁻³ can be produced by the methodof annealing the Ga-doped n-type ZnO single crystal film having Cusupplied on the film surface. In fact, the depth profile shown in thelower column of FIGS. 4 and 6 demonstrate that the acceptorconcentration N_(a) of Samples 1 to 5 is 1.0×10¹⁷ cm⁻³ (in the case ofSample 2) to 1.0×10¹⁹ cm⁻³ (in the case of Samples 1, 3, and 4).

A p-type layer can be deemed practical when the acceptor concentrationis at least 1.0×10¹⁷ cm⁻³. Accordingly, the p-type layer obtained in theexperiment is a p-type ZnO based compound semiconductor single crystallayer having the p-type electroconductivity of practical level.

The method of annealing the Ga-doped ZnO single crystal film having Cusupplied on the film surface is capable of producing a Cu and Gaco-doped ZnO single crystal layer which has Cu evenly doped at a highconcentration through the thickness of the layer and which has p-typeelectroconductivity of practical level. This method has also enabled theproduction by annealing at a low temperature.

The alternate laminate structure (Ga-doped ZnO single crystal filmhaving Cu supplied on the film surface) exhibiting n-typeelectroconductivity is converted to p-type electroconductivity byannealing after increase in the resistance. For example, in the case ofSample 1, the specimen is converted to p-type, by conducing annealing at650° C. for 30 minutes to prepare a specimen exhibiting a highresistance (see graphs in the upper row of FIG. 4), namely, by conducingvisualized step of increasing the resistance, and then conductingfurther annealing for 40 minutes to thereby accomplish the conversion tothe p-type (see graphs in the lower row of FIG. 4). However, thealternate laminate structure is also converted to p-type when thepre-annealing specimen is subjected continuous annealing at 650° C. for70 minutes, and in this process, the alternate laminate structure may bedeemed to have undergone latent increase in the resistance before theconversion to the p-type. Similarly, the alternate laminate structurecould be converted to the p-type through latent increase in theresistance by annealing in the atmosphere, for example, by annealing thepre-annealing specimen of Sample 2 at 650° C. for 30 minutes, thepre-annealing specimen of Sample 3 at 590° C. for 12 minutes, or thepre-annealing specimen of Sample 4 at 600° C. for 50 minutes.

However, it is also possible to consider that the alternate laminatestructure is converted to the p-type not only through the latent orvisualized increase in the resistance but also through the subsequentinsulation, and the process of insulation may be made visualized byselecting an appropriate annealing condition. Accordingly, theconversion to the p-type of the alternate laminate structure may bedescribed as a process through the latent or visualized increase in theresistance and the subsequent latent or visualized insulation process.

The inventors of the present invention found that the alternate laminatestructure reconverted into p-type can again be imparted with n-typeelectroconductivity by further annealing. Accordingly, the annealing maybe finished after the process of increase in the resistance and theconversion into p-type and before the returning to the n-type layer.

The first experiment conducted by the inventors of the present inventiondemonstrated that annealing of the Ga-doped ZnO single crystal filmhaving Cu supplied on the film surface (the alternate laminate structureprepared by alternately repeating the step of forming the Ga-doped ZnOsingle crystal film and the Cu attaching step) results in the increaseof the resistance and subsequent formation of the p-type ZnO layerco-doped with Cu and Ga. Next, Example 1 wherein a ZnO based compoundsemiconductor light emitting element is produced by using the Cu and Gaco-doped ZnO layer for the p-type semiconductor layer is described.

FIGS. 9A and 9B are schematic flow charts showing production method ofthe ZnO based compound semiconductor light emitting element in theExample 1. It is to be noted that the present invention can be appliednot only to the light-emitting elements but also to a wide range ofsemiconductor elements while the light-emitting elements are describedin the Examples.

As shown in FIG. 9A, the production method of the ZnO based compoundsemiconductor light emitting element of Example 1 comprises the steps offorming an n-type ZnO based compound semiconductor layer above asubstrate (step S101), and the step of forming a p-type ZnO basedcompound semiconductor layer above the n-type ZnO based compoundsemiconductor layer formed in step S101 (step S102).

In addition, as shown in FIG. 9B, the step of forming a p-type ZnO basedcompound semiconductor layer of step S102 comprises two steps, namely,step S102 a and step S102 b.

In the step of forming a p-type ZnO based compound semiconductor layer(step S102), a Ga-doped n-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystalfilm having Cu supplied on the film surface is first prepared (step S102a). In an exemplary such preparation, a Ga-doped n-type Mg_(x)Zn_(1-x)O(0≦x≦0.6) single crystal film is formed, and Cu is then supplied on thefilm surface.

Next, the Ga-doped n-type Mg_(x)Zn_(1-x)O single crystal film preparedin step S102 a is annealed to form a p-type film co-doped with Cu and Ga(step S102 b). By this annealing, the Ga-doped n-type Mg_(x)Zn_(1-x)Osingle crystal film is converted to p-type through latent or visualizedincrease of the resistance.

FIG. 9C is schematic cross sectional views of the semiconductor layerillustrating the formation of the p-type ZnO based compoundsemiconductor layer (step S102). In step S102 a, the Ga-doped n-typeMg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film 31 having Cu 32 suppliedon the film surface is prepared. In step S102 b, the Ga-doped n-typeMg_(x)Zn_(1-x)O single crystal film 31 having the Cu 32 attached theretois annealed. This annealing facilitates diffusion of the Cu 32 in theGa-doped n-type Mg_(x)Zn_(1-x)O single crystal film 31, and Cu and Gaco-doped p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film 33 isthereby formed. The formation of the Cu and Ga co-doped p-typeMg_(x)Zn_(1-x)O single crystal film 33 is associated with the precedingincrease in resistance of the Ga-doped n-type Mg_(x)Zn_(1-x)O singlecrystal film 31 caused by diffusion of the Cu 32. More specifically,annealing conditions may be adequately selected to directly convert theGa-doped n-type Mg_(x)Zn_(1-x)O single crystal film 31 having the Cu 32supplied on the film surface to the p-type Mg_(x)Zn_(1-x)O singlecrystal film 33 (conversion to p-type layer through latent increase inthe resistance), or alternatively, to first form the Cu and Ga co-dopedn-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film having a resistancehigher than that of the Ga-doped n-type Mg_(x)Zn_(1-x)O single crystalfilm 31, and then conduct the further annealing to thereby form the Cuand Ga co-doped p-type Mg_(x)Zn_(1-x)O single crystal film 33(conversion to p-type layer through visualized increase in theresistance).

It is to be noted that the conversion into p-type of the Ga-doped n-typeMg_(x)Zn_(1-x)O single crystal film 31 may be considered as a processthrough the steps of increase in the resistance, insulation, andconversion into the p-type. When understood in this way, this processmay be conceived that, in step S102 b, the Ga-doped n-typeMg_(x)Zn_(1-x)O single crystal film 31 is first converted to exhibithigher resistance in latent or visualized way, and then insulated inlatent or visualized way to subsequently exhibit p-typeelectroconductivity.

As shown FIG. 9D, Step S102 b may also be described as a processcomprising the step of annealing the Ga-doped n-type Mg_(x)Zn_(1-x)O(0≦x≦0.6) single crystal film having Cu supplied on the film surface toincrease its resistance (step S102 b ₁) and the step of annealingGa-doped n-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film whoseresistance has been increased in step S102 b ₁ to form a p-type filmco-doped with Cu and Ga (step S102 b ₂).

FIG. 10 is a flow chart showing a production method of the ZnO basedcompound semiconductor light emitting element by Example 1 from anotherpoint of view. In this flow chart, step S102 in FIG. 9A, namely, thestep of forming the p-type ZnO based compound semiconductor layercomprises 4 steps of step S202 a, step S202 b, step S202 c, and stepS202 d.

In the step of forming the p-type ZnO based compound semiconductor layer(step S102), Zn, 0, optional Mg, and Ga are supplied to form theGa-doped n-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film (step S202a). Next, Cu is supplied on the Ga-doped n-type Mg_(x)Zn_(1-x)O(0≦x≦0.6) single crystal film formed in step S202 a (step S202 b). StepS202 a and step S202 b are alternately repeated to form the laminatestructure (step S202 c), and then, the laminate structure formed in stepS202 c is annealed to form the p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) layerdoped with Cu and Ga (step S202 d).

It is to be noted that the n-type ZnO based compound semiconductorlaminate structure by Example 1 is prepared by steps S202 a to step S202c.

Next, Examples 2 to 4 are described. Examples 2 to 4 are application ofExample 1.

Production of a ZnO based compound semiconductor light emitting elementhaving a homo-structure of Example 2 is described by referring FIGS. 11Aand 11B. FIG. 11A is a schematic cross sectional view of the ZnO basedcompound semiconductor light emitting element produced by the productionmethod of Example 2.

A ZnO buffer layer 2 having a thickness of 30 nm was formed on a ZnOsubstrate 1 at a growth temperature of 300° C. by using a Zn flux F_(Zn)of 0.15 nm/s (J_(Zn)=9.9×10¹⁴ atoms/cm²s) and irradiating O radical beamat an RF power of 300 W and a O₂ flow rate of 2.0 sccm (J_(O)=8.1×10¹⁴atoms/cm²s). The ZnO buffer layer 2 was annealed at 900° C. for 10minutes for improving crystallinity and surface evenness of the ZnObuffer layer 2.

Zn, O, and Ga were simultaneously supplied on the ZnO buffer layer 2 ata growth temperature of 900° C. to form an n-type ZnO layer 3 having athickness of 150 nm (for example, step S101 in FIG. 9A). Zn was suppliedat a Zn flux F_(Zn) of 0.15 nm/s (J_(Zn)=9.9×10¹⁴ atoms/cm²s), and the Oradical beam was irradiated at an RF power of 250 W and an O₂ flow rateof 1.0 sccm (J_(O)=4.0×10¹⁴ atoms/cm²s), and Ga cell temperature was460° C. The n-type ZnO layer 3 had a Ga concentration of, for example,1.5×10¹⁸ cm⁻³.

An undoped ZnO active layer 4 having a thickness of 15 nm was depositedon the n-type ZnO layer 3 at a growth temperature of 900° C. and a Znflux F_(Zn) of 0.03 nm/s (J_(Zn)=2.0×10¹⁴ atoms/cm²s). The O radicalbeam was irradiated at an RF power of 300 W and an O₂ flow rate of 2.0sccm (J_(O)=8.1×10¹⁴ atoms/cm²s).

Subsequently, a Cu and Ga co-doped p-type ZnO layer 5 was formed on theundoped ZnO active layer 4 (Step S102 in FIG. 9A).

First, substrate temperature was set to 300° C., and Ga-doped n-type ZnOsingle crystal film having Cu supplied on the surface was prepared bysupplying Zn, O and Ga at a timing different from Cu at the same shuttersequence as the pre-annealing specimen of Sample 1 (see FIG. 2B). Morespecifically, each of the step of depositing a Ga-doped ZnO singlecrystal film by supplying Zn, O, and Ga and the step of supplying Cu onthe Ga-doped ZnO single crystal film were alternately repeated for 140times to form an alternate laminate structure having a thickness of 480nm. In other words, the alternate laminate structure may be regarded asa laminate of 140 Ga-doped n-type ZnO single crystal films each suppliedwith Cu on its surface disposed one on another in thickness direction.

Each growth period for Ga-doped ZnO single crystal film was set at 16seconds, and each Cu supplying period was 10 seconds. The Ga-doped ZnOsingle crystal film was deposited by using a Zn flux F_(Zn) of 0.17 nm/s(J_(Zn)=1.1×10¹⁵ atoms/cm²s), and irradiating the O radical beam at anRF power of 300 W and an O₂ flow rate of 2.0 sccm (J_(O)=8.1×10¹⁴atoms/cm²s), and the Ga cell temperature T_(Ga) was 490° C. The VI/IIflux ratio was 0.74. The cell temperature in the Cu supplying stepT_(Cu), was 930° C., and the Cu flux F_(Cu), was 0.0015 nm/s.

FIG. 11B is a schematic cross sectional view of the alternate laminatestructure 5A. The alternate laminate structure 5A has a structurewherein a Ga-doped ZnO single crystal films 5 a and a Cu layers 5 b arealternately laminated one on another (a structure wherein the Ga-dopedZnO single crystal films 5 a having Cu supplied on the film surface aredisposed one on another in thickness direction). The Ga-doped ZnO singlecrystal film 5 a has a thickness of approximately 3.3 nm, and the Culayer 5 b has a thickness of up to 1 atomic layer, for example, about1/20 atomic layer (so that approximately 5% of the surface of theGa-doped ZnO single crystal film 5 a is covered with Cu). The alternatelaminate structure 5A (the Ga-doped ZnO single crystal film 5 a havingCu supplied on the film) has n-type electroconductivity, and donorconcentration N_(d) is, for example, about 1.0×10²⁰ cm⁻³.

Next, the Ga-doped ZnO single crystal film having Cu supplied on thefilm surface 5 a (alternate laminate structure 5A) was annealed to formthe Cu-doped p-type film (Cu and Ga co-doped p-type ZnO layer 5). Forexample, annealing may be conducted in the atmosphere at 650° C. for 70minutes to diffuse Cu of the Cu layer 5 b into the Ga-doped ZnO singlecrystal film 5 a to convert the alternate laminate structure 5Aexhibiting n-type electroconductivity to the one exhibiting p-type.Under such annealing conditions, the Ga-doped ZnO single crystal film 5a is converted to the one exhibiting p-type through latent increase inthe resistance.

Alternatively, the annealing may be conducted in the atmosphere at 650°C. for 30 minutes to form a Ga-doped ZnO single crystal film 5 a havinga visually increased resistance, and then conducting additionalannealing in the atmosphere at 650° C. for 40 minutes to thereby formthe Ga-doped ZnO single crystal film 5 a exhibiting p-typeelectroconductivity.

An n electrode 6 n was subsequently formed on the rear surface of theZnO substrate 1. A p electrode 6 p was formed on the Cu and Ga co-dopedp-type ZnO layer 5, and a bonding electrode 7 was formed on the pelectrode 6 p. The n electrode 6 n may be formed by depositing an Aulayer having a thickness of 500 nm on a Ti layer having a thickness 10nm. The p electrode 6 p was formed by depositing a Au layer having athickness of 10 nm on a Ni layer having a size of 300 μm square and athickness of 1 nm, and the bonding electrode 7 was formed by depositinga Au layer having a size of 100 μm square and a thickness of 500 nm. TheZnO based compound semiconductor light emitting element was therebyformed by the method of Example 2.

FIG. 11A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 2. The ZnO based compound semiconductor light emittingelement of Example 2 comprises an n-type ZnO based compoundsemiconductor layer (the n-type ZnO layer 3), a ZnO based compoundsemiconductor active layer formed above the n-type ZnO based compoundsemiconductor layer (the undoped ZnO active layer 4), a p-type ZnO basedcompound semiconductor layer formed above the ZnO based compoundsemiconductor active layer (the Cu and Ga co-doped p-type ZnO layer 5),an n electrode electrically connected to the n-type ZnO based compoundsemiconductor layer (the n electrode 6 n), and a p electrodeelectrically connected to the p-type ZnO based compound semiconductorlayer (the p electrode 6 p).

The Cu and Ga co-doped p-type ZnO layer 5 is a p-type ZnO single crystallayer co-doped with Cu and Ga. In the Cu and Ga co-doped p-type ZnOlayer 5, the Cu concentration [Cu] is at least 1.0×10¹⁹ cm⁻³ and lessthan 1.0×10²¹ cm⁻³, and for example, 2.2×10²⁰ cm⁻³, and the [Cu] isapproximately constant in thickness direction. The Ga concentration [Ga]is for example, 3.4×10¹⁹ cm⁻³, and [Ga] is approximately constant inthickness direction. The Cu concentration [Cu] and the Ga concentration[Ga] are in the relation: 0.9 [Cu]/[Ga]<100, and preferably2≦[Cu]/[Ga]≦50. In the Cu and Ga co-doped p-type ZnO layer 5 of Example2, [Cu]/[Ga] is 6.5. The Cu and Ga co-doped p-type ZnO layer 5 of thesemiconductor light emitting element of Example 2 is a p-type ZnO layerhaving a high Cu concentration which is evenly doped through itsthickness.

The production method of Example 2 is capable of producing a Cu and Gaco-doped ZnO single crystal layer which has Cu evenly doped at a highconcentration through the thickness of the layer and which has p-typeelectroconductivity of practical level. This method has also enabled theproduction by annealing at a low temperature.

In the first experiment and Example 2, the layer formed was the Cu andGa co-doped p-type ZnO layer. A Cu-doped p-type film (Cu and Ga co-dopedp-type Mg_(x)Zn_(1-x)O (0<x≦0.6) single crystal film) may also beproduced by annealing a Ga-doped n-type Mg_(x)Zn_(1-x)O (0<x≦0.6) singlecrystal film having Cu supplied on the film surface.

An exemplary preparation of a Ga-doped n-type Mg_(x)Zn_(1-x)O (0<x≦0.6)single crystal film having Cu supplied on the film surface is explainedby referring to FIG. 12. The film prepared is an alternate laminatestructure comprising alternately deposited Ga-doped n-typeMg_(x)Zn_(1-x)O (0<x≦0.6) single crystal film and Cu layer.

FIG. 12 is a time chart of an exemplary shutter sequence of the Zn cell,the Mg cell, the O cell, the Ga cell, and the Cu cell during formationof the alternate laminate structure.

In the formation of the alternate laminate structure, the step ofdepositing the Ga-doped Mg_(x)Zn_(1-x)O (0<x≦0.6) single crystal filmconducted by opening the Zn cell shutter, the Mg cell shutter, the Ocell shutter, and the Ga cell shutter while closing the Cu cell shutter,and the Cu attaching step conducted by closing the Zn cell shutter, theMg cell shutter, the O cell shutter, and the Ga cell shutter whileopening the Cu cell shutter are alternately repeated.

In the case shown in FIG. 12, the step of forming the Ga-dopedMg_(x)Zn_(1-x)O single crystal film is designed so that the period whenZn cell shutter is open include the period when the Mg cell shutter, theO cell shutter, and the Ga cell shutter are open. More specifically,opening and closing of the Mg cell shutter, the O cell shutter, and theGa cell shutter are simultaneously conducted while the Zn cell shutteris opened before the opening of the Mg cell shutter, the O cell shutter,and the Ga cell shutter and closed after the closing of the Mg cellshutter, the O cell shutter, and the Ga cell shutter.

For example, each open period of the Mg cell shutter, the O cellshutter, and the Ga cell shutter is 16 seconds. The Zn cell shutter isopened and closed 1 second before and after the open period of the Mgcell shutter, the O cell shutter, and the Ga cell shutter, andtherefore, each open period of the Zn cell shutter is 18 seconds. The 16seconds when all of the Zn cell shutter, the Mg cell shutter, the O cellshutter, and the Ga cell shutter is each growth period of the Ga-dopedMg_(x)Zn_(1-x)O single crystal film. Each open period of the Cu cellshutter was 10 seconds.

Since simultaneous supplying of the O radical and the Cu is avoided andthe surface of the Ga-doped Mg_(x)Zn_(1-x)O single crystal film iscovered with Zn before and after the Cu attachment step, direct reactionbetween the O radical and the Cu is suppressed.

When Mg is supplied with Zn, at least one of the open period of the Zncell shutter and the open period of the Mg cell shutter preferablyincludes the open period of the O cell shutter in view of suppressingthe reaction the O radical and the Cu. In addition, in view ofcontrolling Mg composition in the Ga-doped Mg_(x)Zn_(1-x)O singlecrystal film, the open period of the Zn cell shutter should preferablyinclude the open period of the Mg cell shutter and O cell shutter.

Annealing of the Ga-doped n-type Mg_(x)Zn_(1-x)O (0<x≦0.6) singlecrystal film having the Cu supplied on the film surface (the alternatelaminate structure) results in the increase of the resistance, and then,in the production of the Cu and Ga co-doped p-type Mg_(x)Zn_(1-x)O(0<x≦0.6) single crystal film.

Next, a ZnO based compound semiconductor light emitting element with adouble heterostructure having a Cu and Ga co-doped p-typeMg_(x)Zn_(1-x)O (0<x≦0.6) single crystal layer is described by referringto Examples 3 and 4.

FIG. 13A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 3.

Zn and O were simultaneously supplied on the surface of the ZnOsubstrate 11 to deposit a ZnO buffer layer 12 having a thickness of, forexample, 30 nm. Exemplary conditions used in depositing the ZnO bufferlayer 12 include a growth temperature of 300° C., a Zn flux F_(Zn) of0.15 nm/s, and the O radical beam irradiation at an RF power 300 W andan O₂ flow rate of 2.0 sccm. Annealing at 900° C. for 10 minutes wasconducted to improve crystallinity and surface evenness of the ZnObuffer layer 12.

Zn, O, and Ga were simultaneously supplied on the surface of the ZnObuffer layer 12 to deposit an n-type ZnO layer 13 having a thickness of150 nm, for example, at a temperature of 900° C. The Zn flux F_(Zn) was0.15 nm/s and the O radical beam was irradiated at an RF power of 250 Wand an O₂ flow rate of 1.0 sccm, and Ga cell temperature was 460° C. Then-type ZnO layer 13 had a Ga concentration of, for example, 1.5×10¹⁸cm⁻³.

Zn, Mg, and O were simultaneously supplied on the surface of the n-typeZnO layer 13 to deposit an n-type MgZnO layer 14 having a thickness of,for example, 30 nm. Exemplary conditions used in the deposition includea temperature of 900° C., a Zn flux F_(Zn) of 0.1 nm/s, a Mg flux F_(Mg)of 0.025 nm/s, and the O radical beam irradiation at an RF power of 300W and an O₂ flow rate of 2.0 sccm. The Mg composition of the n-typeMgZnO layer 14 is, for example, 0.3.

Zn and O were simultaneously supplied on the surface of the on then-type MgZnO layer 14 to deposit a ZnO active layer 15 having athickness 10 nm at a temperature of 900° C. The Zn flux F_(Zn) was 0.1nm/s, and the O radical beam was irradiated at an RF power of 300 W andan O₂ flow rate of 2.0 sccm.

As shown in FIG. 13B, the active layer 15 may comprise a quantum wellstructure formed by alternately depositing a MgZnO barrier layer 15 band a ZnO well layer 15 w one on another instead of the single layer ZnOlayer.

An alternate laminate structure was formed on the active layer 15 byreducing the substrate temperature, for example, to 300° C. andalternately repeating the step of depositing the Ga-doped MgZnO singlecrystal film and the Cu attachment step (Ga-doped n-type MgZnO singlecrystal film having Cu supplied on the film surface was prepared). Theshutter sequence of the Zn cell, the Mg cell, the O cell, the Ga thecell, and Cu cell used in forming the alternate laminate structure maybe, for example, the same as the one shown in FIG. 12.

For example, each growth period in the step of depositing the Ga-dopedMgZnO single crystal film was 16 seconds, and each Cu supplying periodin the Cu attachment step was 10 seconds. In the step of depositing theGa-doped MgZnO single crystal film, the Zn flux F_(Zn) was 0.15 nm/s,the Mg flux F_(Mg) was 0.03 nm/s, and the O radical beam was irradiatedat an RF power of 300 W and an O₂ flow rate of 2.0 sccm, and the Ga celltemperature T_(Ga) was 498° C. The VI/II flux ratio was 0.72. In thestep of supplying Cu, the Cu cell temperature T_(Cu) was 930° C. and theCu flux F_(Cu) was 0.0015 nm/s. Each of the step of depositing theGa-doped MgZnO single crystal film and the Cu attachment steps werealternately repeated for 60 times to deposit an alternate laminatestructure having a thickness of 200 nm. The alternate laminate structuremay also be deemed as a laminate prepared by disposing 60 layers of theGa-doped n-type MgZnO single crystal film having Cu supplied on the filmsurface in the thickness direction.

FIG. 13C is a schematic cross sectional view of the alternate laminatestructure 16A. The alternate laminate structure 16A has a structurewherein a Ga-doped MgZnO single crystal films 16 a and a Cu layers 16 bare alternately laminated one on another (a structure wherein theGa-doped MgZnO single crystal films 16 a having Cu supplied on the filmsurface are disposed one on another in thickness direction). TheGa-doped MgZnO single crystal film 16 a has a thickness of approximately3.3 nm, and the Cu layer 16 b has a thickness of up to 1 atomic layer,for example, about 1/20 atomic layer (so that approximately 5% of thesurface of the Ga-doped MgZnO single crystal film 16 a is covered withCu). The alternate laminate structure 16A (the Ga-doped MgZnO singlecrystal film 16 a having Cu supplied on the film) has n-typeelectroconductivity, and donor concentration N_(d) is, for example,about 7.5×10¹⁹ cm⁻³.

Next, a Cu-doped p-type film (the Cu and Ga co-doped p-type MgZnO layer16) was formed on the active layer 15 by annealing the Ga-doped MgZnOsingle crystal film 16 a having Cu supplied on the film surface (thealternate laminate structure 16A). The alternate laminate structure 16Ashowing n-type electroconductivity may be converted to exhibit p-type bydiffusing Cu in the Cu layer 16 b into the Ga-doped MgZnO single crystalfilm 16 a by conducting the annealing, for example, in the atmosphere at650° C. for 20 minutes. Under such annealing conditions, the Ga-dopedMgZnO single crystal film 16 a is converted to the one exhibiting p-typethrough latent increase in the resistance.

Alternatively, the Ga-doped MgZnO single crystal film 16 a may beconverted to exhibit p-type by conducting the annealing, for example, inthe atmosphere at 650° C. for 10 minutes to visually increase resistanceof the Ga-doped MgZnO single crystal film 16 a, and further annealing inthe atmosphere at 650° C. for 10 minutes.

Mg composition in the Cu and Ga co-doped p-type MgZnO layer 16 is, forexample, 0.3.

An n electrode 17 n was formed on the rear surface of the ZnO substrate11. A p electrode 17 p was formed on the Cu and Ga co-doped p-type MgZnOlayer 16, and a bonding electrode 18 was formed on the p electrode 17 p.The n electrode 17 n may be formed, for example, by depositing an Aulayer having a thickness 500 nm on a Ti layer having a thickness of 10nm, and the p electrode 17 p was formed by depositing a Au layer havinga thickness of 10 nm on a Ni layer having a size of 300 μm square and athickness of 1 nm, and the bonding electrode 18 was formed by depositinga Au layer having a size of 100 μm square to a thickness of 500 nm. TheZnO based compound semiconductor light emitting element was therebyformed by the method of Example 3.

In Example 3, the ZnO based compound semiconductor light emittingelement was produced by using the ZnO substrate 11. However, the elementmay also be prepared by using an electroconductive substrate such asMgZnO substrate, GaN substrate, SiC substrate, and Ga₂O₃ substrate.

FIG. 13A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 3. The ZnO based compound semiconductor light emittingelement of Example 3 comprises an n-type ZnO based compoundsemiconductor layer (for example, the n-type ZnO layer 13), an ZnO basedcompound semiconductor active layer formed above the n-type ZnO basedcompound semiconductor layer (the active layer 15), a p-type ZnO basedcompound semiconductor layer formed above the ZnO based compoundsemiconductor active layer (the Cu and Ga co-doped p-type MgZnO layer16), an n electrode electrically connected to the n-type ZnO basedcompound semiconductor layer (the n electrode 17 n), and p electrodeelectrically connected to the p-type ZnO based compound semiconductorlayer (the p electrode 17 p).

The Cu and Ga co-doped p-type MgZnO layer 16 is a p-type MgZnO singlecrystal layer co-doped with Cu and Ga. In the Cu and Ga co-doped p-typeMgZnO layer 16, the Cu concentration [Cu] is at least 1.0×10¹⁹ cm⁻³ andless than 1.0×10²¹ cm⁻³, and for example, 2.0×10²⁰ cm⁻³, and the [Cu] isapproximately constant in thickness direction. The Ga concentration [Ga]is for example, 3.6×10¹⁹ cm⁻³, and the [Ga] is approximately constant inthickness direction. The Cu concentration [Cu] and the Ga concentration[Ga] are in the relation: 0.9 [Cu]/[Ga]<100, and preferably 2[Cu]/[Ga]≦50. In the Cu and Ga co-doped p-type MgZnO layer 16 of Example3, [Cu]/[Ga] is 5.6. The Cu and Ga co-doped p-type MgZnO layer 16 of thesemiconductor light emitting element of Example 3 is a p-type ZnO layerhaving a high Cu concentration which is evenly doped through itsthickness.

The production method of Example 3 is capable of producing a Cu and Gaco-doped p-type MgZnO layer 16 which has Cu evenly doped at a highconcentration through the thickness of the layer and which has p-typeelectroconductivity of practical level. This method has also enabled theproduction by annealing at a low temperature.

FIG. 14 is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 4. In contrast to Examples 2 and 3 where crystals wereallowed to grow on the electroconductive substrate to form the layer,the crystals are allowed to grow on the insulative substrate.

Mg and O are simultaneously supplied onto a c face sapphire substrate 21which is an insulated substrate to deposit a MgO buffer layer 22 having,a thickness of, for example, 10 nm. In an exemplary embodiment, the MgObuffer layer 22 may be deposited at a temperature of 650° C. with a Mgflux F_(Mg) of 0.05 nm/s by irradiating the O radical beam at an RFpower of 300 W and an O₂ flow rate of 2.0 sccm. The MgO buffer layer 22functions as a polarity control layer which facilitates deposition ofthe overlying ZnO based compound semiconductor layer with the Zn face asits surface.

Zn and O are simultaneously supplied on the MgO buffer layer 22 todeposit a ZnO buffer layer 23 having a thickness of 30 nm, for example,at a temperature of 300° C. and a Zn flux F_(Zn) of 0.15 nm/s byirradiating the O radical beam at an RF power of 300 W and an O₂ flowrate of 2.0 sccm. The ZnO buffer layer 23 deposits at the Zn face.Annealing is conducted at 900° C. for 30 minutes to improvecrystallinity and surface evenness of the ZnO buffer layer 23.

Zn, O and Ga are simultaneously supplied on the ZnO buffer layer 23 todeposit an n-type ZnO layer 24 having a thickness of, for example, 1.5μm. In an exemplary embodiment, the n-type ZnO layer 24 is deposited ata temperature of 900° C. and a Zn flux F_(Zn) of 0.05 nm/s byirradiating the O radical beam at an RF power of 300 W and an O₂ flowrate of 2.0 sccm, with the Ga cell at a temperature of 480° C.

Zn, Mg, and O are simultaneously supplied on the n-type ZnO layer 24 todeposit an n-type MgZnO layer 25 having a thickness of, for example, 30nm. The n-type MgZnO layer 25 may be deposited at a temperature of 900°C., a Zn flux F_(2n) of 0.1 nm/s, and a Mg flux F_(Mg) of 0.025 nm/s byirradiating the O radical beam at an RF power of 300 W and an O₂ flowrate of 2.0 sccm. Mg composition of the n-type MgZnO layer 25 is, forexample, 0.3.

A ZnO active layer 26 having a thickness of, for example, 10 nm isdeposited on the n-type MgZnO layer 25. The conditions used for thedeposition may be the same as the deposition of the active layer 15 inExample 3. A quantum well structure may be employed instead of themonolayer ZnO layer.

A Cu and Ga co-doped p-type MgZnO layer 27 is formed on the active layer26. The method used may be, for example, the same as the method used inthe formation of the Cu and Ga co-doped p-type MgZnO layer 16 used inExample 3.

The c face sapphire substrate 21 of Example 4 is an insulatingsubstrate, and the n electrode can not be formed on the rear surface ofthe substrate 21. Accordingly, the Cu and Ga co-doped p-type MgZnO layer27 is etched from its upper surface until the n-type ZnO layer 24 isexposed to thereby form an n electrode 28 n on the thus exposed n-typeZnO layer 24. In the meanwhile, a p electrode 28 p is formed on the Cuand Ga co-doped p-type MgZnO layer 27, and a bonding electrode 29 isformed on the p electrode 28 p.

The n electrode 28 n is formed by depositing a Au layer having athickness of 500 nm on a Ti layer having a thickness of 10 nm, and the pelectrode 28 p is formed by depositing a Au layer having a thickness of10 nm on a Ni layer having a thickness of 0.5 nm. The bonding electrode29 is formed by a Au layer having a thickness of 500 nm. The ZnO basedcompound semiconductor light emitting element thus produced by themethod of Example 4.

The Cu and Ga co-doped p-type MgZnO layer 27 of the ZnO based compoundsemiconductor light emitting element of Example 4 is a p-type ZnO basedcompound semiconductor single crystal layer exhibiting propertiessimilar to those of the Cu and Ga co-doped p-type MgZnO layer 16 ofExample 3.

Next, the second experiment of the inventors of the present invention isdescribed. After intensive study, the inventors of the present inventionfound that the Cu-doped ZnO single crystal film having Ga supplied onthe film (the alternate laminate structure) is converted to a p-typefilm by annealing. The experiment will be described for Sample 6 andSample 7.

FIG. 15A is a schematic cross sectional view of the pre-annealingspecimen. The pre-annealing specimen of Sample 6 was prepared by theprocedure as described below.

A ZnO buffer layer 62 and an undoped ZnO layer 63 were formed on a ZnOsubstrate 61 in this order. The method used in the formation of the ZnObuffer layer 62 and the undoped ZnO layer 63 is the same as the methodused in the formation of the ZnO buffer layer 52 and the undoped ZnOlayer 53 in Sample 1.

Zn, O, and Cu were supplied at a timing different from Ga on the undopedZnO layer 63 at different timing to form an alternate laminate structure64. The alternate laminate structure 64 was formed at a temperature of250° C.

FIG. 15B is a time chart showing shutter sequence of the Zn cell, the Ocell, the Cu cell, and the Ga cell in forming the alternate laminatestructure.

In forming the alternate laminate structure 64, the step of forming theCu-doped ZnO single crystal film by opening the Zn cell shutter, the Ocell shutter, and the Cu cell shutter and closing the Ga cell shutterand the step of Ga attachment (the step of forming the Ga layer) byclosing the Zn cell shutter, the 0 cell shutter, and the Cu cell shutterand opening the Ga cell shutter were alternately repeated.

In the step of forming the Cu-doped ZnO single crystal film, the openingand closing of the O cell shutter and the Cu cell shutter aresimultaneously conducted, and the Zn cell shutter is opened beforeopening the O cell shutter and the Cu cell shutter and closed afterclosing the O cell shutter and the Cu cell shutter, and in other words,the open period of the Zn cell shutter include the open period of the Ocell shutter and the Cu cell shutter.

In the preparation of the pre-annealing specimen of Sample 6, the openperiod of the O cell shutter and the Cu cell shutter was 8 seconds foreach opening, and the open period of the Zn cell shutter was extended 1second before and after the open period of the O cell shutter and the Cucell shutter. The open period of the Zn cell shutter was 10 seconds foreach opening, and the 8 second period when all of the Zn cell shutter,the O cell shutter, and the Cu cell shutter were open was the periodallowed for each Cu-doped ZnO single crystal film growth period. Theopen period of the Ga cell shutter was 8 seconds for each opening.

Each of the step of forming the Cu-doped ZnO single crystal film and theGa attachment step were alternately repeated for 60 times to deposit thealternate laminate structure 64 having a thickness of 133 nm. In theformation of the Cu-doped ZnO single crystal film, the Zn flux F_(Zn)was 0.17 nm/s (J_(Zn)=1.1×10¹⁵ atoms/cm²s), and the O radical beam wasirradiated at an RF power 300 W and an O₂ flow rate 2.0 sccm(J_(O)=8.1×10¹⁴ atoms/cm²s), and the Cu cell temperature T_(c), was 990°C. The VI/II flux ratio was 0.74 (Zn rich condition). In the Gaattachment step, the Ga cell temperature T_(Ga) was 540° C.

FIG. 15C is a schematic cross sectional view of the alternate laminatestructure 64. The alternate laminate structure 64 has a structurewherein Cu-doped ZnO single crystal films 64 a and Ga layers 64 b arealternately laminated one on another. This laminate structure may alsobe regarded as a laminate structure comprising 60 layers of the Cu-dopedZnO single crystal films 64 a each having the Ga supplied thereondisposed one on another in thickness direction.

The Cu-doped ZnO single crystal film 64 a has a thickness ofapproximately 2.2 nm, and the Ga layer 64 b has a thickness (Gaattachment thickness) of up to 1 atomic layer, for example, about 1/16atomic layer. In this case, Ga coverage of the surface of the Cu-dopedZnO single crystal film 64 a will be approximately 6%.

FIG. 15D is a schematic cross sectional view of the Cu-doped ZnO singlecrystal film 64 a and the Ga layer 64 b. For example, the Ga layer 54 bhaving a thickness of about 1/16 atomic layer is formed by Ga attachedto a part of the surface of the Cu-doped ZnO single crystal film 64 a.For the simplicity of the drawing, the alternate laminate structure isshown by the layer structure of FIG. 15C including such embodiment ofthe Ga attachment.

FIG. 16A shows graphs of CV profile, depth profile of the impurityconcentration, and depth profile of [Cu] and [Ga] measured by SIMS forthe alternate laminate structure 64 of the pre-annealing specimen ofSample 6. The upper row is the graph showing the CV profile, the middlerow is the graph showing the depth profile of impurity concentration,and the lower row is the graph showing the depth profile of [Cu] and[Ga] measured by SIMS. The x and y axes of the graphs in the upper andmiddle rows are the same as the graphs in the upper and lower rows ofFIG. 3. The x and y axes of the graph in the lower row are the same asthe graphs in the lower row of FIG. 5 for Sample 4.

In the graph of the upper row, 1/C² increases with the increase in thevoltage, and this means that the Cu-doped ZnO single crystal film 64 ahaving Ga supplied on the surface of the layer (alternate laminatestructure 64) has n-type electroconductivity.

The graph in the middle row indicates that the alternate laminatestructure 64 has an impurity concentration (donor concentration) N_(d)of 1.0×10²¹ cm⁻³ to 5.0×10²¹ cm⁻³.

The graph in the lower row indicates that the alternate laminatestructure 64 has a Cu concentration [Cu] of 5.02×10²⁰ cm⁻³ and a Gaconcentration [Ga] of 3.67×10²⁰ cm⁻³. The value of [Cu]/[Ga] is 1.37.

Next, Sample 6 was subjected to the annealing in oxygen atmosphere at aflow rate of 1 L/min at 560° C. for 26 minutes.

FIG. 16B shows, from top to down, graphs showing CV profile, depthprofile of the impurity concentration, and depth profile of [Cu] and[Ga] measured by SIMS for the position where the alternate laminatestructure 64 had been formed of the post-annealing specimen of Sample 6.The x and y axes of the graphs are the same as those of FIG. 16A.

In the graph of the upper row, 1/C² decreases with the increase in thevoltage, and this means that the position where alternate laminatestructure 64 had been formed has p-type electroconductivity.

The graph in the middle row indicates that the position where alternatelaminate structure 64 had been formed (the position where the p-typelayer is formed) in the post-annealing specimen of Sample 6 has animpurity concentration (acceptor concentration) N_(a) of 5.0×10¹⁷ cm⁻³to 4.0×10¹⁸ cm⁻³.

The graph in the lower row indicates that the position where alternatelaminate structure 64 had been formed (the position where the p-typelayer is formed) has a Cu concentration [Cu] of 4.68×10²⁰ cm⁻³, a Gaconcentration [Ga] of 4.13×10²⁰ cm⁻³, and both [Cu] and [Ga] areapproximately constant through the thickness of the p-type layer. Cu andGa are evenly diffused. The value of [Cu]/[Ga] is 1.13.

FIG. 17 shows RHEED images of p-type layer from the [11-20] directionand the [1-100] direction. The RHEED image shows streak pattern,indicating formation of the single crystal layer with flat surface andgood crystallinity.

Use of low temperature (up to 300° C., for example, 250° C.) and Zn rich(Group II rich) conditions in the deposition of the alternate laminatestructure 64 has resulted in the suppression of the CuO crystal phaseformation, and the alternate deposition of the Cu-doped ZnO film 64 aand the Ga layer 64 b has promoted migration of Zn on the Ga surface,and hence, growth of the single crystal of the alternate laminatestructure 64 (Cu-doped ZnO film 64 a).

Next, Sample 7 is described. In the preparation of the pre-annealingspecimen of Sample 7, each of the step of depositing the Cu-doped ZnOsingle crystal film and the Ga attaching step are repeated 60 times toform an alternate laminate structure having a thickness of 100 nm. TheCu-doped ZnO single crystal film was formed under the same conditions asthe pre-annealing specimen of Sample 6 except that the VI/II flux ratiowas 0.82 (Zn rich condition) by controlling the Zn flux F_(Zn) to 0.15nm/s (J_(Zn)=9.9×10¹⁴ atoms/cm²s), the Cu cell temperature T_(Cu) was970° C., and the Ga cell temperature T_(Ga) in the Ga attaching step was550° C.

FIG. 18A shows, from top to down, graphs showing CV profile, depthprofile of the impurity concentration, and depth profile of [Cu] and[Ga] measured by SIMS for the alternate laminate structure of thepost-annealing specimen of Sample 7. The x and y axes of the graphs arethe same as those of FIG. 16A.

In the graph of the upper row, 1/C² increases with the increase in thevoltage, and this means that the Cu-doped ZnO single crystal film havingGa supplied on the film surface (alternate laminate structure) hasn-type electroconductivity.

The graph in the middle row indicates that the alternate laminatestructure has an impurity concentration (donor concentration) N_(d) of1.0×10²¹ cm⁻³ to 3.0×10²¹ cm⁻³.

The graph in the lower row indicates that the alternate laminatestructure has a Cu concentration [Cu] of 3.95×10²⁰ cm⁻³ and a Gaconcentration [Ga] of 4.97×10²⁰ cm⁻³. The value of [Cu]/[Ga] value is0.79.

Sample 7 was subjected to the annealing in oxygen atmosphere at a flowrate of 1 L/min at 630° C. for 10 minutes.

FIG. 18B shows, from top to down, graphs of CV profile, depth profile ofthe impurity concentration, and depth profile of [Cu] and [Ga] measuredby SIMS for the position where the alternate laminate structure had beenformed of the post-annealing specimen of Sample 7. The x and y axes ofthe graphs are the same as those of FIG. 16B.

In the graph of the upper row, 1/C² decreases with the increase in thevoltage, and this means that the position where the alternate laminatestructure had been formed has p-type electroconductivity.

The graph in the middle row indicates that the position where thealternate laminate structure had been formed (the position where thep-type layer is formed) in the post-annealing specimen of Sample 7 hasan impurity concentration (acceptor concentration) N_(a) of 1.0×10¹⁸cm⁻³ to 6.5×10¹⁸ cm⁻³.

The graph in the lower row indicates that the position where thealternate laminate structure had been formed (the position where thep-type layer is formed) has a Cu concentration [Cu] of 2.98×10²⁰ cm⁻³, aGa concentration [Ga] of 5.41×10²⁰ cm⁻³, and both [Cu] and [Ga] areapproximately constant through the thickness of the p-type layer exceptfor the part near the surface significantly affected by the mattersadsorbed on the surface. Cu and Ga are evenly diffused. The value of[Cu]/[Ga] is 0.55.

The results of the Samples 6 and 7 demonstrate that the alternatelaminate structure (Cu-doped ZnO single crystal film) of the secondexperiment is n-type in its as-grown state, and it becomes a p-typestructure by the annealing. In the as-grown state, Cu in the Cu-dopedZnO single crystal film is not functioning as an acceptor. Conceivably,the annealing results generation of Cu⁺ which functions as an acceptorwith the even diffusion of the Ga of the Ga layer into the Cu-doped ZnOsingle crystal film, and the p-type ZnO single crystal layer co-dopedwith Cu and Ga is thereby formed (conversion to p-type). The alternatelaminate structure is converted to p-type after experiencing increase inthe resistance.

The annealing conditions (for example, temperature, time, andatmosphere) used for conversion to p-type should be different dependingon the thickness of the alternate laminate structure or the Cu-doped ZnOsingle crystal film, the Cu concentration [Cu], the Ga concentration[Ga], and the [Cu]/[Ga] of the alternate laminate structure, and thelike.

In the first experiment, the [Cu]/[Ga] of the alternate laminatestructure of the pre-annealing specimen was greater than 1 whereas the[Cu]/[Ga] of the alternate laminate structure of the pre-annealingspecimen in the second experiment is 1.37 (Sample 6) and 0.79 (Sample7). In the production method of the p-type ZnO based compoundsemiconductor layer of the second experiment 2, a p-type layer is formedeven if the [Cu]/[Ga] of the alternate laminate structure of thepre-annealing specimen was up to 1.

In addition, when the inventors of the present invention prepared thesamples of the first experiment which has the donor concentration N_(d)in the alternate laminate structure of pre-annealing specimen and theacceptor concentration N_(a) at the position corresponding to thealternate laminate structure in the post-annealing specimensubstantially equal to Sample 6 for comparison with Sample 6, thesamples of the first experiment required an annealing temperature of600° C., while the conversion to the p-type was realized in Sample 6 at560° C. This means that the method of the second experiment is capableof forming the p-type layer by annealing at a temperature lower than themethod of the first experiment. Accordingly, the method of the secondexperiment is capable of more effectively reducing the risk of, forexample, formation of donor-type point defect such as oxygen vacancy byhigh temperature annealing, decrease in the Cu concentration and the Gaconcentration in the p-type layer associated with diffusion of Cu and Gato the exterior of the p-type layer, and loss of steepness at the p-ninterface associated with the diffusion of the Cu and the Ga to theunderlying layer (n-type layer). For example, the method of the secondexperiment is capable of producing a ZnO based compound semiconductorelement having a steeper p-n interface than the Samples of the firstexperiment.

The results of the second experiment also indicates that, Cu can beevenly doped in the thickness direction at least to a concentration ofless than 1.0×10²¹ cm⁻³ so that the Cu will be at a concentration highenough, namely, at 1.0×10¹⁹ cm⁻³ or higher, for example, by the methodof annealing the Cu-doped n-type ZnO single crystal film having Gasupplied on the film surface. The method of annealing the Cu-dopedn-type ZnO single crystal film having Ga supplied on the film surface iscapable of producing a p-type layer having an acceptor concentration ofat least 1.0×10¹⁷ cm⁻³ and less than 1.0×10¹⁹ cm⁻³. The p-type layerobtained in the second experiment is a p-type ZnO based compoundsemiconductor single crystal layer having the p-type electroconductivityof practical level.

The method of annealing the Cu-doped ZnO single crystal film having Gasupplied on the film surface is capable of producing a Cu and Gaco-doped ZnO single crystal layer which has Cu evenly doped at a highconcentration through the thickness of the layer and which has p-typeelectroconductivity of practical level. In the Cu and Ga co-doped ZnOsingle crystal layer, Ga is also evenly doped through the thickness ofthe layer. The Cu and Ga co-doped ZnO single crystal layer can beproduced by conducting the annealing at a lower temperature.

The inventors of the present invention found also for the secondexperiment that the alternate laminate structure converted into p-typecan again be imparted with n-type electroconductivity by furtherannealing. Accordingly, the annealing may be finished after the processof increase in the resistance and the conversion into p-type and beforethe returning to the n-type layer.

As described above, the second experiment has demonstrated that a p-typeZnO layer co-doped with Cu and Ga can be produced by alternatelyrepeating the step of depositing the Cu-doped ZnO single crystal filmand Ga attachment step to produce the alternate laminate structure, andthereafter annealing the thus prepared alternate laminate structure.

FIGS. 19A and 19B are schematic flow charts of the production method ofZnO based compound semiconductor light emitting element according toExample 5.

As shown in FIG. 19A, the production method of the ZnO based compoundsemiconductor light emitting element by Example 5 comprises the step offorming an n-type ZnO based compound semiconductor layer above thesubstrate (step S301) and the step of forming a p-type ZnO basedcompound semiconductor layer above the n-type ZnO based compoundsemiconductor layer formed in the step S301 (step S302).

As shown in FIG. 19B, the step S302 of forming the p-type ZnO basedcompound semiconductor layer comprises four steps of step S302 a, stepS302 b, step S302 c, and step S302 d.

In the step of forming the p-type ZnO based compound semiconductor layer(step S302), Zn, 0, optional Mg, and Cu are supplied to form theCu-doped n-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film (step S302a). Next, Ga is supplied on the Cu-doped n-type Mg_(x)Zn_(1-x)O(0≦x≦0.6) single crystal film formed in step S302 a (step S302 b). StepS302 a and step S302 b are alternately repeated to form the laminatestructure (step S302 c), and then, the laminate structure formed in stepS302 c is annealed to form the p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) layerdoped with Cu and Ga (step S302 d).

It is to be noted that the n-type ZnO based compound semiconductorlaminate structure by Example 5 is prepared by steps S302 a to step S302c.

Next, Examples 6 to 8 are described. Examples 6 to 8 are application ofExample 5.

Production of a ZnO based compound semiconductor light emitting elementhaving a homo-structure of Example 6 is described by referring FIGS. 20Aand 20B. In FIGS. 20A and 20B, reference number 91 represents a ZnOsubstrate, 92 represents a ZnO buffer layer, 93 represents an n-type ZnOlayer, 94 represents an undoped ZnO active layer, 95 represents a Cu andGa co-doped p-type ZnO layer, 95A represents an alternate laminatestructure, 95 a represents a Cu-doped ZnO single crystal film, 95 brepresents a Ga layer, 96 n represents an n electrode, 96 p represents ap electrode, and 97 represents a bonding electrode.

FIG. 20A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 6.

In Example 6, the ZnO based compound semiconductor light emittingelement may be produced by repeating the procedure of Example 2 exceptfor the Cu and Ga co-doped p-type ZnO layer 95.

In the formation of the Cu and Ga co-doped p-type ZnO layer 95, Zn, O,and Cu are supplied at a timing different from Ga at a substratetemperature of 250° C. by using the same shutter sequence (see FIG. 15B)as the preparation of the pre-annealing specimen of Sample 7 to form analternate laminate structure. More specifically, each of the step ofsupplying Zn, O, and Cu to deposit the Cu-doped ZnO single crystal film(step S302 a in FIG. 19B) and the step of supplying Ga on the Cu-dopedZnO single crystal film (step S302 b in FIG. 19B) were alternatelyrepeated 60 times to form an alternate laminate structure having athickness of 100 nm (step S302 c in FIG. 19B). Each growth period of theCu-doped ZnO single crystal film and each Ga supplying period were 8seconds. In the deposition of the Cu-doped ZnO single crystal film, theZn flux F_(Zn) was 0.15 nm/s (J_(Zn)=9.9×10¹⁴ atoms/cm²s), and the Oradical beam was irradiated at an RF power of 300 W and an O₂ flow rateof 2.0 sccm (J_(O)=8.1×10¹⁴ atoms/cm²s). The Cu cell temperature T_(Cu)was 970° C., and the VI/II flux ratio was 0.82. In Ga supplying step,the Ga cell temperature T_(Ga) was 550° C.

FIG. 20B is a schematic cross sectional view of an alternate laminatestructure 95A. The alternate laminate structure 95A has a structurewherein a Cu-doped ZnO single crystal films 95 a and a Ga layers 95 bare alternately laminated one on another. The Cu-doped ZnO singlecrystal film 95 a has a thickness of about 1.7 nm, and the Ga layer 95 bhas a thickness of up to 1 atomic layer, for example, about 1/15 atomiclayer (corresponding to about 7% surface coverage by the Ga of theCu-doped ZnO single crystal film 95 a). The alternate laminate structure95A exhibits n-type electroconductivity, and the donor concentrationN_(d) is, for example, 1.0×10²¹ cm⁻³.

Next, the alternate laminate structure was annealed to form a p-type ZnOsingle crystal layer co-doped with Cu and Ga (step S302 d of FIG. 19B).The alternate laminate structure 95A exhibiting n-typeelectroconductivity can be converted to a ZnO layer having p-typeelectroconductivity (Cu and Ga co-doped p-type ZnO layer 95), forexample, by annealing in oxygen atmosphere at a flow rate of 1 L/min at630° C. for 10 minutes.

The Cu and Ga co-doped p-type ZnO layer 95 of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 6 is a Cu and Ga co-doped p-type ZnO based compoundsemiconductor single crystal layer which may be obtained by annealing analternate laminate structure 95A having a [Cu]/[Ga] of up to 1, forexample, 0.79. The Cu concentration [Cu] is at least 1.0×10¹⁹ cm⁻³ andless than 1.0×10²¹ cm⁻³, for example, 2.98×10²⁰ cm⁻³, and thisconcentration is approximately constant in thickness direction. The Gaconcentration [Ga] is, for example, 5.41×10²⁰ cm⁻³, and thisconcentration is approximately constant in thickness direction. In theCu and Ga co-doped p-type ZnO layer 95 of Example 6, the [Cu]/[Ga] is0.55.

The production method of Example 6 is capable of producing a Cu and Gaco-doped ZnO single crystal layer 95 which has Cu and Ga evenly doped ata high concentration through the thickness of the layer and which hasp-type electroconductivity of practical level. This method has alsoenabled the production by annealing at a low temperature. The ZnO basedcompound semiconductor light emitting element produced by the productionmethod of Example 6 has, for example, a steep p-n interface.

A Cu and Ga co-doped p-type ZnO layer was formed in the secondexperiment and Example 6. A Cu and Ga co-doped Mg_(x)Zn_(1-x)O (0<x≦0.6)single crystal layer exhibiting p-type electroconductivity can beproduced by annealing the alternate laminate structure formed byalternately conducing the step of depositing the Cu-doped n-typeMg_(x)Zn_(1-x)O (0<x≦0.6) single crystal film and the Ga attachmentstep.

FIG. 21 is a time chart showing shutter sequence of the Zn cell, the Mgcell, the O cell, the Cu cell, and the Ga cell in forming the alternatelaminate structure in the formation of the Cu and Ga co-doped p-typeMg_(x)Zn_(1-x)O (0<x≦0.6) single crystal layer.

In forming the alternate laminate structure, the step of forming theCu-doped Mg_(x)Zn_(1-x)O (0<x≦0.6) single crystal film by opening the Zncell shutter, the Mg cell shutter, the O cell shutter, and the Cu cellshutter and closing the Ga cell shutter and the step of Ga attachment byclosing the Zn cell shutter, the Mg cell shutter, the O cell shutter,and the Cu cell shutter and opening the Ga cell shutter were alternatelyrepeated.

In the case shown in FIG. 21, the step of forming the Cu-dopedMg_(x)Zn_(1-x)O single crystal film is designed so that the period whenZn cell shutter is open include the period when the Mg cell shutter, theO cell shutter, and the Cu cell shutter are open. More specifically,opening and closing of the Mg cell shutter, the O cell shutter, and theCu cell shutter are simultaneously conducted while the Zn cell shutteris opened before the opening of the Mg cell shutter, the O cell shutter,and the Cu cell shutter and closed after the closing of the Mg cellshutter, the O cell shutter, and the Cu cell shutter.

For example, each open period of the Mg cell shutter, the O cellshutter, and the Cu cell shutter is 8 seconds. The Zn cell shutter isopened and closed 1 second before and after the open period of the Mgcell shutter, the O cell shutter, and the Cu cell shutter, andtherefore, each open period of the Zn cell shutter is 10 seconds. The 8seconds when all of the Zn cell shutter, the Mg cell shutter, the O cellshutter, and the Cu cell shutter is each growth period of the Cu-dopedMg_(x)Zn_(1-x)O single crystal film. Each open period of the Ga cellshutter is 8 seconds.

Next, Examples 7 and 8 is described by referring to FIGS. 22A to 22C andFIG. 23. In Examples 7 and 8, a ZnO based compound semiconductor lightemitting element with a double heterostructure having a Cu and Gaco-doped p-type Mg_(x)Zn_(1-x)O (0<x≦0.6) single crystal layer isproduced. FIGS. 22A to 22C corresponds to FIGS. 13A to 13C of Example 3.FIG. 23 corresponds to FIG. 14 of Example 4.

In FIG. 22A to FIG. 22C, and FIG. 23, reference number 101 represents aZnO substrate, 102 represents a ZnO buffer layer, 103 represents ann-type ZnO layer, 104 represents an n-type MgZnO layer, 105 representsan active layer, 105 b represents a MgZnO barrier layer, 105 wrepresents a ZnO well layer, 106 represents a Cu and Ga co-doped p-typeMgZnO layer, 106A represents an alternate laminate structure, 106 arepresents a Cu-doped MgZnO single crystal film, 106 b represents a Galayer, 107 n represents an n electrode, 107 p represents a p electrode,108 represents a bonding electrode, 111 represents a c face sapphiresubstrate, 112 represents a MgO buffer layer, 113 represents a ZnObuffer layer, 114 represents an n-type ZnO layer, 115 represents ann-type MgZnO layer, 116 represents an active layer, 117 represents a Cuand Ga co-doped p-type MgZnO layer, 118 n represents an n electrode, 118p represents a p electrode, and 119 represents a bonding electrode.

FIG. 22A is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 7.

In Example 7, the ZnO based compound semiconductor light emittingelement may be produced by repeating the procedure of Example 3 exceptfor the Cu and Ga co-doped p-type MgZnO layer 106.

In forming the Cu and Ga co-doped p-type MgZnO layer 106, the substratetemperature was reduced, for example, to 250° C. and the step ofdepositing the Cu-doped n-type MgZnO single crystal film and the Gaattachment step were alternately repeated to form an alternate laminatestructure on the active layer 105. The shutter sequence of the Zn cell,the Mg cell, the O cell, the Cu the cell, and Ga cell used in formingthe alternate laminate structure may be, for example, the same as theone shown in FIG. 21.

For example, each growth period in the Cu-doped MgZnO single crystalfilm growth step was 8 seconds, and each Ga supplying period in the Gaattachment step was 8 seconds. In the formation of the Cu-doped MgZnOsingle crystal film, the Zn flux F_(Zn) was 0.15 nm/s and the Mg fluxF_(Mg) was 0.04 nm/s, and the O radical beam was irradiated at an RFpower of 300 W and an O₂ flow rate of 2.0 sccm, and the Cu celltemperature T_(Cu), was 990° C. The VI/II flux ratio was 0.70. In the Gasupplying step, the Ga cell temperature T_(Ga) was 540° C. Each of thestep of forming the Cu-doped MgZnO single crystal film and the Gaattachment step were alternately repeated for 60 times to deposit thealternate laminate structure having a thickness of 120 nm.

As in the case of Example 3, the active layer 105 may comprise a quantumwell structure formed by alternately depositing a MgZnO barrier layer105 b and a ZnO well layer 105 w one on another instead of the singlelayer ZnO layer as shown in FIG. 22B.

FIG. 22C is a schematic cross sectional view of an alternate laminatestructure 106A. The alternate laminate structure 106A has a structurewherein a Cu-doped MgZnO single crystal film 106 a and a Ga layer 106 bare alternately laminated one on another. The Cu-doped MgZnO singlecrystal film 106 a has a thickness of approximately 2.0 nm, the Ga layer106 b has a thickness of up to 1 atomic layer, for example, about 1/16atomic layer (corresponding to Ga surface coverage of the Cu-doped MgZnOsingle crystal film 106 a of approximately 6%). The alternate laminatestructure 106A exhibits n-type electroconductivity, and the donorconcentration N_(d) is, for example, 1.5×10²⁰ cm⁻³.

Next, the alternate laminate structure 106A was annealed to form a Cuand Ga co-doped p-type MgZnO layer 106 on the active layer 105. Thealternate laminate structure 106A exhibiting n-type electroconductivitycan be converted to a single crystal layer exhibiting p-typeelectroconductivity (a Cu and Ga co-doped p-type MgZnO layer 106) byconducting the annealing in an oxygen atmosphere at a flow rate of 1L/min at 610° C. for 10 minutes. The Mg composition in the Cu and Gaco-doped p-type MgZnO layer 106 is, for example, 0.3.

The Cu and Ga co-doped p-type MgZnO layer 106 of the ZnO based compoundsemiconductor light emitting element produced in Example 7 is a Cu andGa co-doped p-type ZnO based compound semiconductor single crystal layerwhich may be obtained by annealing an alternate laminate structure 106Ahaving a [Cu]/[Ga] of at least 0.5, for example, 1.40. The Cuconcentration [Cu] is at least 1.0×10′^(s) cm⁻³ and less than 1.0×10²¹cm⁻³, for example, 5.0×10²⁰ cm⁻³, and this concentration isapproximately constant in thickness direction. The Ga concentration [Ga]is, for example, 4.0×10²⁰ cm⁻³, and this concentration is approximatelyconstant in thickness direction. In the Cu and Ga co-doped p-type MgZnOlayer 106 of Example 7, the [Cu]/[Ga] is 1.25.

The production method of Example 7 is capable of producing a Cu and Gaco-doped MgZnO single crystal layer 106 which has Cu and Ga evenly dopedat a high concentration through the thickness of the layer and which hasp-type electroconductivity of practical level. This method has alsoenabled the production by annealing at a low temperature. The ZnO basedcompound semiconductor light emitting element produced by the productionmethod of Example 7 has, for example, a steep p-n interface.

FIG. 23 is a schematic cross sectional view of the ZnO based compoundsemiconductor light emitting element produced by the production methodof Example 8.

In Example 8, the ZnO based compound semiconductor light emittingelement may be produced by repeating the procedure of Example 4 exceptfor the Cu and Ga co-doped p-type MgZnO layer 117.

The Cu and Ga co-doped p-type MgZnO layer 117 may be formed, forexample, by the same procedure as the formation of the Cu and Gaco-doped p-type MgZnO layer 106 in Example 7.

The Cu and Ga co-doped p-type MgZnO layer 117 of the ZnO based compoundsemiconductor light emitting element of Example 8 is a p-type ZnO basedcompound semiconductor single crystal layer which has similar propertiesas the Cu and Ga co-doped p-type MgZnO layer 106 of Example 7.

The present invention has been described by referring to Experiments andExamples. The present invention, however, is not limited by theseExperiments and Examples.

For example, O radical was used for the source of oxygen in theproduction method of the Examples. The oxygen source used may also beozone, a polar oxidizing agent such as H₂O or alcohol, or other highlyoxidative gas.

In the production method of the Examples, the Ga-doped n-typeMg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film having Cu supplied on thefilm surface and the Cu-doped n-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) singlecrystal film having Ga supplied on the film surface were formed by MBE.However, the method used in forming such layer is not limited the MBE,and the layer may be formed, for example, by vacuum deposition orsputtering.

In addition, in the first experiment and Examples 1 to 4, the Ga-dopedn-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film having Cu suppliedon the film surface was annealed to form the Cu-doped p-type film (Cuand Ga co-doped p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film).When the Ga (a Group 13 element)-doped n-type Mg_(x)Zn_(1-x)O singlecrystal film having the Cu (Group 11 element) attached is annealed,binding of the Cu in its monovalent state (Cu⁺) with O which is a Group16 element is facilitated, and this results in the higher tendency ofthe generation of the monovalent Cu⁺ which functions as an acceptorcompared to the divalent Cu²⁺, and hence, conversion of the Ga-dopedn-type Mg_(x)Zn_(1-x)O single crystal film to the p-type. Accordingly,Ag which is a Group 11 element which may have different valances as inthe case of Cu may be used instead of Cu or simultaneously with the Cu.Similarly, a Group 13 element such as B, Al, or In can be used for theGa, and the Group 13 element used may be a Group 13 element selectedfrom the group consisting of B, Ga, Al, and In.

For the same reason, Ag which is a Group 11 element which may havedifferent valances as in the case of Cu may be used instead of Cu orsimultaneously with the Cu in the second experiment and Examples 5 to 8.Similarly, a Group 13 element such as B, Al, or In can be used for theGa, and the Group 13 element used may be a Group 13 element selectedfrom the group consisting of B, Ga, Al, and In.

It is to be noted that in the Cu and Ga co-doped p-type Mg_(x)Zn_(1-x)O(0≦x≦0.6) single crystal film, Cu in its monovalent state and Ga in itstrivalent state substitute the Zn or the Mg site, and the Cu and the Gaelectrically attracts each other. Because of such mutual electricalattraction between the Cu and the Ga, Cu in its monovalent statefunctioning as an acceptor has higher tendency of substituting the Zn orthe Mg site compared to Cu in the divalent state.

In other words, the p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film(p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film co-doped with theGroup 11 element and the Group 13 element) wherein the Zn or Mg site issubstituted by Group 11 element which is Cu and/or Ag in its monovalentstate or at least one Group 13 element selected from the groupconsisting of B, Ga, Al, and In in its trivalent state, and the Group 11element and the Group 13 element are electrically attracting each otheris produced by the method of annealing Mg_(x)Zn_(1-x)O (0≦x≦0.6) singlecrystal film doped with at least one Group 13 element selected from thegroup consisting of B, Ga, Al, and In having Cu and/or Ag supplied onthe film surface and the method of annealing Mg_(x)Zn_(1-x)O (0≦x≦0.6)single crystal film doped with Cu and/or Ag having at least one Group 13element selected from the group consisting of B, Ga, Al, and In suppliedon the film surface.

As readily understood by those skilled in the art, variousmodifications, improvements, combinations, and the like are possible forthe present invention.

It is to be noted that the findings (1) to (3) as described below havebeen obtained in the related application of the inventors of the presentinvention (Japanese Patent Application No. 2012-41096) wherein theCu-doped p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) layer is produced by the stepsof (a) forming Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film and (13)supplying Cu on the Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal film.

(1) Thickness of the Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal filmformed in each step (α) is preferably up to 10 nm for avoidingunfavorable crystallinity.

(2) In the step (α), the Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal filmis preferably formed in stoichiometric conditions (wherein VI/II fluxratio is 1) or Group II rich conditions (wherein VI/II flux ratio isless than 1) for realizing high evenness and good crystallinity, andmore preferably, under the condition that the VI/II flux ratio is atleast 0.5 and less than 1.

(3) In the step (a), the Mg_(x)Zn_(1-x)O (0≦x≦0.6) single crystal filmis preferably formed at a temperature (substrate temperature) of atleast about 200° C. and up to 350° C. in view of realizing good crystalgrowth.

In the step of preparing the Ga-doped n-type Mg_(x)Zn_(1-x)O (0≦x≦0.6)single crystal film having Cu supplied on the film surface and the stepof preparing the Cu-doped n-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) singlecrystal film having Ga supplied on the film surface in the presentinvention, a p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) layer having high evennessand good crystallinity can be realized when the Ga-doped n-typeMg_(x)Zn_(1-x)O single crystal film and the Cu-doped n-typeMg_(x)Zn_(1-x)O single crystal film are deposited under the conditions(1) to (3) as described above.

FIG. 24 is a table summarizing conditions used in forming the Ga-dopedn-type Mg_(x)Zn_(1-x)O single crystal film in Examples 2 to 4.

As shown in this table, the conditions of (1) to (3) are satisfied inall of Examples 2 to 4. Accordingly, the p-type Mg_(x)Zn_(1-x)O(0≦x≦0.6) layer produced by the production method of Examples 2 to 4 hashigh evenness as well as good crystallinity.

FIG. 25 is a table summarizing conditions used in forming the Cu-dopedn-type Mg_(x)Zn_(1-x)O single crystal film in Examples 6 to 8.

As shown in this table, the conditions of (1) to (3) are satisfied inall of Examples 6 to 8. Accordingly, the p-type Mg_(x)Zn_(1-x)O(0≦x≦0.6) layer produced by the production method of Examples 6 to 8 hashigh evenness as well as good crystallinity.

The inventors of the present invention examined the surface by usingimages taken by an atomic force microscope (AFM). The examinationconfirmed that the surface of the p-type Mg_(x)Zn_(1-x)O (0≦x≦0.6) layerhas a surface evenness higher than the surface of the alternate laminatestructure. Annealing results a p-type ZnO based compound semiconductorlayer having an improved evenness.

The p-type ZnO based compound semiconductor layer produced by the methodof Examples may be used, for example, in a light emitting diode (LED) ora laser diode (LD) emitting a light having a short wavelength (thewavelength range of ultraviolet to blue), various products produced bysuch LED or LD (for example, indicators, LED displays, and light sourcefor CV/DVD), and also, in white LED and various products produced usingsuch while LED (for example, light fixtures, indicators, displays, andbacklight of various displays), and ultraviolet sensor.

What we claim are:
 1. A method for producing a p-type ZnO based compoundsemiconductor layer comprising the steps of (a) supplying (i) Zn, (ii)O, (iii) optionally Mg, and (iv) a Group 11 element which is Cu and/orAg to form a Mg_(x)Zn_(1-x)O single crystal film doped with the Group 11element, wherein 0≦x≦0.6; (b) supplying at least one Group 13 elementselected from the group consisting of B, Ga and Al on theMg_(x)Zn_(1-x)O single crystal film, wherein 0≦x≦0.6, wherein supplyingZn is carried out in an open period of a Zn cell shutter, supplying O iscarried out in an open period of an O cell shutter, supplying at leastone of B, Ga or Al is carried out in an open period of at least one of aB, Ga or Al cell shutter and supplying Cu and/or Ag is carried out in anopen period of a Cu and/or Ag cell shutter, and wherein the open periodof the Zn cell shutter includes the open period of the O cell shutterand the open period of the Cu and/or Ag cell shutter, and does notinclude the open period of the at least one of the B, Ga or Al cellshutter; and the open period of the O cell shutter or the open period ofthe Cu and/or Ag cell shutter does not coincide with a beginning of theopen period of the Zn cell shutter and an ending of the open period ofthe Zn cell shutter; (c) alternately carrying out the steps (a) and (b)to form a laminate structure; and (d) annealing the laminate structureto form a p-type Mg_(x)Zn_(1-x)O layer co-doped with the Group 11element, and the Group 13 element, wherein 0≦x≦0.6.
 2. The method forproducing a p-type ZnO based compound semiconductor layer according toclaim 1, wherein the step (a) is carried out by molecular beam epitaxy(MBE) at a substrate temperature of up to 350° C.
 3. The method forproducing a p-type ZnO based compound semiconductor layer according toclaim 1, wherein the step (a) is carried out under a condition that aVI/II flux ratio is at least 0.5 and less than 1, wherein the conditionwherein the VI/II flux ratio is less than 1 is referred to as a Group IIrich condition, the condition wherein the VI/II flux ratio is equal to 1is referred to as a stoichiometric condition, and the condition whereinthe VI/II flux ratio is greater than 1 is referred to as a Group VI richcondition.
 4. A method for producing a ZnO based compound semiconductorelement comprising the steps of forming an n-type ZnO based compoundsemiconductor layer above a substrate; and forming a p-type ZnO basedcompound semiconductor layer above the n-type ZnO based compoundsemiconductor layer; wherein the step of forming the p-type ZnO basedcompound semiconductor layer comprises the steps of (a) supplying (i)Zn, (ii) O, (iii) optionally Mg, and (iv) a Group 11 element which is Cuand/or Ag to form a Mg_(x)Zn_(1-x)O single crystal film doped with theGroup 11 element, wherein 0≦x≦0.6; (b) supplying at least one Group 13element selected from the group consisting of B, Ga and Al on theMg_(x)Zn_(1-x)O single crystal film, wherein 0≦x≦0.6, wherein supplyingZn is carried out in an open period of a Zn cell shutter, supplying O iscarried out in an open period of an O cell shutter, supplying at leastone of B, Ga or Al is carried out in an open period of at least one of aB, Ga or Al cell shutter and supplying Cu and/or Ag is carried out in anopen period of a Cu and/or Ag cell shutter, and wherein the open periodof the Zn cell shutter includes the open period of the 0 cell shutterand the open period of the Cu and/or Ag cell shutter, and does notinclude the open period of the at least one of the B, Ga or Al cellshutter; and the open period of the O cell shutter or the open period ofthe Cu and/or Ag cell shutter does not coincide with a beginning of theopen period of the Zn cell shutter and the end an ending of the openperiod of the Zn cell shutter; (c) alternately carrying out the steps(a) and (b) to form a laminate structure; and (d) annealing the laminatestructure to form a p-type Mg_(x)Zn_(1-x)O layer co-doped with the Group11 element, and the Group 13 element, wherein 0≦x≦0.6.
 5. The method forproducing a ZnO based compound semiconductor element according to claim4, wherein the step (a) is conducted by molecular beam epitaxy (MBE) ata substrate temperature of up to 350° C.
 6. The method for producing aZnO based compound semiconductor element according to claim 4, whereinthe step (a) is carried out under a condition that a VI/II flux ratio isat least 0.5 less than 1, wherein the condition wherein the VI/II fluxratio is less than 1 is referred to as a Group II rich condition, thecondition wherein the VI/II flux ratio is equal to 1 is referred to as astoichiometric condition, and the condition wherein the VI/II flux ratiois greater than 1 is referred to as a Group VI rich condition.